General Solvent-dependent Strategy toward Enhanced Oxygen Reduction Reaction in Graphene/Metal Oxide Nanohybrids: Effects of Nitrogen-containing Solvent

PubMed Central

Kao, Wei-Yao; Chen, Wei-Quan; Chiu, Yu-Hsiang; Ho, Yu-Hsuan; Chen, Chun-Hu

2016-01-01

A general solvent-dependent protocol directly influencing the oxygen reduction reaction (ORR) in metal oxide/graphene nanohybrids has been demonstrated. We conducted the two-step synthesis of cobalt oxide/N-doped graphene nanohybrids (CNG) with solvents of water, ethanol, and dimethylformamide (DMF), representing tree typical categories of aqueous, polar organic, and organic N-containing solvents commonly adopted for graphene nanocomposites preparation. The superior ORR performance of the DMF-hybrids can be attributed to the high nitrogen-doping, aggregation-free hybridization, and unique graphene porous structures. As DMF is the more effective N-source, the spectroscopic results support a catalytic nitrogenation potentially mediated by cobalt-DMF coordination complexes. The wide-distribution of porosity (covering micro-, meso-, to macro-pore) and micron-void assembly of graphene may further enhance the diffusion kinetics for ORR. As the results, CNG by DMF-synthesis exhibits the high ORR activities close to Pt/C (i.e. only 8 mV difference of half-wave potential with electron transfer number of 3.96) with the better durability in the alkaline condition. Additional graphene hybrids comprised of iron and manganese oxides also show the superior ORR activities by DMF-synthesis, confirming the general solvent-dependent protocol to achieve enhanced ORR activities. PMID:27853187

Surface mediated assembly of small, metastable gold nanoclusters.

PubMed

Pettibone, John M; Osborn, William A; Rykaczewski, Konrad; Talin, A Alec; Bonevich, John E; Hudgens, Jeffrey W; Allendorf, Mark D

2013-07-21

The unique properties of metallic nanoclusters are attractive for numerous commercial and industrial applications but are generally less stable than nanocrystals. Thus, developing methodologies for stabilizing nanoclusters and retaining their enhanced functionality is of great interest. We report the assembly of PPh3-protected Au9 clusters from a heterogeneous mixture into films consisting of sub 3 nm nanocluster assemblies. The depositing nanoclusters are metastable in solution, but the resulting nanocluster assemblies are stabilized indefinitely in air or fresh solvent. The films exhibit distinct structure from Au nanoparticles observed by X-ray diffraction, and film dissolution data support the preservation of small nanoclusters. UV-Vis spectroscopy, electrospray ionization mass spectrometry, X-ray photoelectron spectroscopy and electron microscopy are used to elucidate information regarding the nanocluster formation and assembly mechanism. Preferential deposition of nanocluster assemblies can be achieved on multiple substrates, including polymer, Cr, Si, SiO2, SiNx, and metal-organic frameworks (MOFs). Unlike other vapor phase coating processes, nanocluster assembly on the MIL-68(In) MOF crystal is capable of preferentially coating the external surface and stabilizing the crystal structure in hydrothermal conditions, which should enhance their storage, separation and delivery capabilities.

Mesophase and size manipulation of itraconazole liquid crystalline nanoparticles produced via quasi nanoemulsion precipitation.

PubMed

Mugheirbi, Naila A; Tajber, Lidia

2015-10-01

The fabrication of drug nanoparticles (NPs) with process-mediated tunable properties and performances continues to grow rapidly during the last decades. This study investigates the synthesis and phase tuning of nanoparticulate itraconazole (ITR) mesophases using quasi nanoemulsion precipitation from acetone/water systems to seek out an alternative pathway to the nucleation-based NP formation. ITR liquid crystalline (LC) phases were formed and nematic-smectic mesomorphism was achieved via controlling solvent:antisolvent temperature difference (ΔTS:AS). The use of ΔTS:AS=49.5°C was associated with a nematic assembly, while intercalated smectic A layering was observed at ΔTS:AS=0°C, with both phases confined in the nanospheres at room temperature. The quasi emulsion system has not been investigated at the nanoscale to date and in contrary to the microscale, quasi nanoemulsion was observed over the solvent:antisolvent viscosity ratios of 1:7-1:1.4. Poly(acrylic acid) in the solvent phase exhibited a concentration dependent interaction when ITR formed NPs. This nanodroplet-based approach enabled the preparation of a stable ITR nanodispersion using Poloxamer 407 at 80°C, which was unachievable before using precipitation via nucleation. Findings of this work lay groundwork in terms of rationalised molecular assembly as a tool in designing pharmaceutical LC NPs with tailored properties. Copyright © 2015 Elsevier B.V. All rights reserved.

Membraneless organelles can melt nucleic acid duplexes and act as biomolecular filters

NASA Astrophysics Data System (ADS)

Nott, Timothy J.; Craggs, Timothy D.; Baldwin, Andrew J.

2016-06-01

Membraneless organelles are cellular compartments made from drops of liquid protein inside a cell. These compartments assemble via the phase separation of disordered regions of proteins in response to changes in the cellular environment and the cell cycle. Here we demonstrate that the solvent environment within the interior of these cellular bodies behaves more like an organic solvent than like water. One of the most-stable biological structures known, the DNA double helix, can be melted once inside the liquid droplet, and simultaneously structures formed from regulatory single-stranded nucleic acids are stabilized. Moreover, proteins are shown to have a wide range of absorption or exclusion from these bodies, and can act as importers for otherwise-excluded nucleic acids, which suggests the existence of a protein-mediated trafficking system. A common strategy in organic chemistry is to utilize different solvents to influence the behaviour of molecules and reactions. These results reveal that cells have also evolved this capability by exploiting the interiors of membraneless organelles.

Morphological Diversity and Polymorphism of Self-Assembling Collagen Peptides Controlled by Length of Hydrophobic Domains

PubMed Central

2015-01-01

Synthetic collagen mimetic peptides are used to probe the role of hydrophobic forces in mediating protein self-assembly. Higher order association is an integral property of natural collagens, which assemble into fibers and meshes that comprise the extracellular matrix of connective tissues. The unique triple-helix fold fully exposes two-thirds of positions in the protein to solvent, providing ample opportunities for engineering interaction sites. Inclusion of just a few hydrophobic groups in a minimal peptide promotes a rich variety of self-assembly behaviors, resulting in hundred-nanometer to micron size nanodiscs and nanofibers. Morphology depends primarily on the length of hydrophobic domains. Peptide discs contain lipophilic domains capable of sequestering small hydrophobic dyes. Combining multiple peptide types result in composite structures of discs and fibers ranging from stars to plates-on-a-string. These systems provide valuable tools to shed insight into the fundamental principles underlying hydrophobicity-driven higher order protein association that will facilitate the design of self-assembling systems in biomaterials and nanomedical applications. PMID:25390880

Microcapsule Structure with a Tunable Textured Surface via the Assembly of Polyoxomolybdate Clusters: A Bioinspired Strategy and Enhanced Activities in Alkene Oxidation.

PubMed

Chilivery, Rakesh; Rana, Rohit Kumar

2017-01-25

A polyamine-mediated bioinspired strategy to assemble Keggin-type phosphomolybdic acid (PMA) clusters is demonstrated for the fabrication of microcapsule (MC) structures with unique surface textures. It involves supramolecular aggregation of polyamines with multivalent anions, which then allows the assembly of negatively charged PMA into MCs in an aqueous medium under ambient conditions. Resembling the role of polyamines in biosilicification of diatoms, the polyamine-anion interaction is shown to be the key for the assembly process. It not only provides structural stability but also facilitates an interesting transition from a smooth to a wrinkled surface alongside a change in the Keggin form to its lacunary form depending on the pH of the medium. Moreover, the presence of isolated PMA units in the hybrid structure enables them to be active in catalyzing the aerobic oxidation of alkenes under solvent-free conditions with better selectivity and reusability. Hence, the assembly approach represents an effective way for heterogenization of PMA-based materials and is expected to find considerable application in the wider hybrid-cluster field.

Role of Small Subunit in Mediating Assembly of Red-type Form I Rubisco

PubMed Central

Joshi, Jidnyasa; Mueller-Cajar, Oliver; Tsai, Yi-Chin C.; Hartl, F. Ulrich; Hayer-Hartl, Manajit

2015-01-01

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is the key enzyme involved in photosynthetic carbon fixation, converting atmospheric CO2 to organic compounds. Form I Rubisco is a cylindrical complex composed of eight large (RbcL) subunits that are capped by four small subunits (RbcS) at the top and four at the bottom. Form I Rubiscos are phylogenetically divided into green- and red-type. Some red-type enzymes have catalytically superior properties. Thus, understanding their folding and assembly is of considerable biotechnological interest. Folding of the green-type RbcL subunits in cyanobacteria is mediated by the GroEL/ES chaperonin system, and assembly to holoenzyme requires specialized chaperones such as RbcX and RAF1. Here, we show that the red-type RbcL subunits in the proteobacterium Rhodobacter sphaeroides also fold with GroEL/ES. However, assembly proceeds in a chaperone-independent manner. We find that the C-terminal β-hairpin extension of red-type RbcS, which is absent in green-type RbcS, is critical for efficient assembly. The β-hairpins of four RbcS subunits form an eight-stranded β-barrel that protrudes into the central solvent channel of the RbcL core complex. The two β-barrels stabilize the complex through multiple interactions with the RbcL subunits. A chimeric green-type RbcS carrying the C-terminal β-hairpin renders the assembly of a cyanobacterial Rubisco independent of RbcX. Our results may facilitate the engineering of crop plants with improved growth properties expressing red-type Rubisco. PMID:25371207

Effect of Solvent Choice on the Self-Assembly Properties of a Diphenylalanine Amphiphile Stabilized by an Ion Pair.

PubMed

Mayans, Enric; Ballano, Gema; Sendros, Javier; Font-Bardia, Merçè; Campos, J Lourdes; Puiggalí, Jordi; Cativiela, Carlos; Alemán, Carlos

2017-07-19

A diphenylalanine (FF) amphiphile blocked at the C terminus with a benzyl ester (OBzl) and stabilized at the N terminus with a trifluoroacetate (TFA) anion was synthetized and characterized. Aggregation of peptide molecules was studied by considering a peptide solution in an organic solvent and adding pure water, a KCl solution, or another organic solvent as co-solvent. The choice of the organic solvent and co-solvent and the solvent/co-solvent ratio allowed the mixture to be tuned by modulating the polarity, the ionic strength, and the peptide concentration. Differences in the properties of the media used to dissolve the peptides resulted in the formation of different self-assembled microstructures (e.g. fibers, branched-like structures, plates, and spherulites). Furthermore, crystals of TFA⋅FF-OBzl were obtained from the aqueous peptide solutions for X-ray diffraction analysis. The results revealed a hydrophilic core constituted by carboxylate (from TFA), ester, and amide groups, and the core was found to be surrounded by a hydrophobic crown with ten aromatic rings. This segregated organization explains the assemblies observed in the different solvent mixtures as a function of the environmental polarity, ionic strength, and peptide concentration. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-assembly of nanocomposite materials

DOEpatents

Brinker, C. Jeffrey; Sellinger, Alan; Lu, Yunfeng

2001-01-01

A method of making a nanocomposite self-assembly is provided where at least one hydrophilic compound, at least one hydrophobic compound, and at least one amphiphilic surfactant are mixed in an aqueous solvent with the solvent subsequently evaporated to form a self-assembled liquid crystalline mesophase material. Upon polymerization of the hydrophilic and hydrophobic compounds, a robust nanocomposite self-assembled material is formed. Importantly, in the reaction mixture, the amphiphilic surfactant has an initial concentration below the critical micelle concentration to allow formation of the liquid-phase micellar mesophase material. A variety of nanocomposite structures can be formed, depending upon the solvent evaporazation process, including layered mesophases, tubular mesophases, and a hierarchical composite coating composed of an isotropic worm-like micellar overlayer bonded to an oriented, nanolaminated underlayer.

Formation of hydroxyl-functionalized stilbenoid molecular sieves at the liquid/solid interface on top of a 1-decanol monolayer.

PubMed

Bellec, Amandine; Arrigoni, Claire; Douillard, Ludovic; Fiorini-Debuisschert, Céline; Mathevet, Fabrice; Kreher, David; Attias, André-Jean; Charra, Fabrice

2014-10-31

Specific molecular tectons can be designed to form molecular sieves through self-assembly at the solid-liquid interface. After demonstrating a model tecton bearing apolar alkyl chains, we then focus on a modified structure involving asymmetric functionalization of some alkyl chains with polar hydroxyl groups in order to get chemical selectivity in the sieving. As the formation of supramolecular self-assembled networks strongly depends on molecule-molecule, molecule-substrate and molecule-solvent interactions, we compared the tectons' self-assembly on graphite for two types of solvent. We demonstrate the possibility to create hydroxylated stilbenoid molecular sieves by using 1-decanol as a solvent. Interestingly, with this solvent, the porous network is developed on top of a 1-decanol monolayer.

Simulation of macromolecule self-assembly in solution: A multiscale approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lavino, Alessio D., E-mail: alessiodomenico.lavino@studenti.polito.it; Barresi, Antonello A., E-mail: antonello.barresi@polito.it; Marchisio, Daniele L., E-mail: daniele.marchisio@polito.it

2015-12-17

One of the most common processes to produce polymer nanoparticles is to induce self-assembly by using the solvent-displacement method, in which the polymer is dissolved in a “good” solvent and the solution is then mixed with an “anti-solvent”. The polymer ability to self-assemble in solution is therefore determined by its structural and transport properties in solutions of the pure solvents and at the intermediate compositions. In this work, we focus on poly-ε-caprolactone (PCL) which is a biocompatible polymer that finds widespread application in the pharmaceutical and biomedical fields, performing simulation at three different scales using three different computational tools: fullmore » atomistic molecular dynamics (MD), population balance modeling (PBM) and computational fluid dynamics (CFD). Simulations consider PCL chains of different molecular weight in solution of pure acetone (good solvent), of pure water (anti-solvent) and their mixtures, and mixing at different rates and initial concentrations in a confined impinging jets mixer (CIJM). Our MD simulations reveal that the nano-structuring of one of the solvents in the mixture leads to an unexpected identical polymer structure irrespectively of the concentration of the two solvents. In particular, although in pure solvents the behavior of the polymer is, as expected, very different, at intermediate compositions, the PCL chain shows properties very similar to those found in pure acetone as a result of the clustering of the acetone molecules in the vicinity of the polymer chain. We derive an analytical expression to predict the polymer structural properties in solution at different solvent compositions and use it to formulate an aggregation kernel to describe the self-assembly in the CIJM via PBM and CFD. Simulations are eventually validated against experiments.« less

Theoretical study on substituent and solvent effects for nanocubes formed with gear-shaped amphiphile molecules.

PubMed

Mashiko, T; Hiraoka, S; Nagashima, U; Tachikawa, M

2017-01-04

Gear-shaped amphiphile molecules (1) recently synthesized by Hiraoka et al. self-assemble into a hexameric structure, nanocubes (1 6 ), in 25% aqueous methanol due to a solvophobic effect. Here we have carried out molecular dynamic simulations to elucidate the stability of these hexameric capsules (1 6 and 2 6 ) in water, 25% aqueous methanol, and methanol. In all solvents, the 1 6 nanocubes are maintained for all trajectories. On the other hand, 2 6 was found to collapse for one trajectory in water and seven trajectories in 25% aqueous methanol. In a pure methanol solvent, 2 6 was found to collapse for all trajectories. The number of collapsed trajectories of 2 6 increased with the amount of methanol in the solvent. We therefore focused on the structure of the π-π stacking between pyridyl groups and the CH-π interactions between the methyl and pyridyl groups within the nanocube. Our study clearly shows the role played by the methanol solvent molecules in the assembly of the nanocube in terms of the substituent and solvent effects at the molecular level, and that these substituent and solvent effects are important for the self-assembly of the nanocubes.

Role of small subunit in mediating assembly of red-type form I Rubisco.

PubMed

Joshi, Jidnyasa; Mueller-Cajar, Oliver; Tsai, Yi-Chin C; Hartl, F Ulrich; Hayer-Hartl, Manajit

2015-01-09

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is the key enzyme involved in photosynthetic carbon fixation, converting atmospheric CO2 to organic compounds. Form I Rubisco is a cylindrical complex composed of eight large (RbcL) subunits that are capped by four small subunits (RbcS) at the top and four at the bottom. Form I Rubiscos are phylogenetically divided into green- and red-type. Some red-type enzymes have catalytically superior properties. Thus, understanding their folding and assembly is of considerable biotechnological interest. Folding of the green-type RbcL subunits in cyanobacteria is mediated by the GroEL/ES chaperonin system, and assembly to holoenzyme requires specialized chaperones such as RbcX and RAF1. Here, we show that the red-type RbcL subunits in the proteobacterium Rhodobacter sphaeroides also fold with GroEL/ES. However, assembly proceeds in a chaperone-independent manner. We find that the C-terminal β-hairpin extension of red-type RbcS, which is absent in green-type RbcS, is critical for efficient assembly. The β-hairpins of four RbcS subunits form an eight-stranded β-barrel that protrudes into the central solvent channel of the RbcL core complex. The two β-barrels stabilize the complex through multiple interactions with the RbcL subunits. A chimeric green-type RbcS carrying the C-terminal β-hairpin renders the assembly of a cyanobacterial Rubisco independent of RbcX. Our results may facilitate the engineering of crop plants with improved growth properties expressing red-type Rubisco. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

Analysis of the Efficiency of Surfactant-Mediated Stabilization Reactions of EGaIn Nanodroplets.

PubMed

Finkenauer, Lauren R; Lu, Qingyun; Hakem, Ilhem F; Majidi, Carmel; Bockstaller, Michael R

2017-09-26

A methodology based on light scattering and spectrophotometry was developed to evaluate the effect of organic surfactants on the size and yield of eutectic gallium/indium (EGaIn) nanodroplets formed in organic solvents by ultrasonication. The process was subsequently applied to systematically evaluate the role of headgroup chemistry as well as polar/apolar interactions of aliphatic surfactant systems on the efficiency of nanodroplet formation. Ethanol was found to be the most effective solvent medium in promoting the formation and stabilization of EGaIn nanodroplets. For the case of thiol-based surfactants in ethanol, the yield of nanodroplet formation increased with the number of carbon atoms in the aliphatic part. In the case of the most effective surfactant system-octadecanethiol-the nanodroplet yield increased by about 370% as compared to pristine ethanol. The rather low overall efficiency of the reaction process along with the incompatibility of surfactant-stabilized EGaIn nanodroplets in nonpolar organic solvents suggests that the stabilization mechanism differs from the established self-assembled monolayer formation process that has been widely observed in nanoparticle formation.

Design, construction, and testing a purpose-built climate-controlled solvent vapor annealing chamber for guided self-assembly of block polymer thin films

NASA Astrophysics Data System (ADS)

Gnabasik, Ryan; Haase, Rustin; Baruth, Andrew

2014-03-01

Despite its efficacy to produce well-ordered, periodic nanostructures, the intricate role multiple parameters play in solvent vapor annealing has not been fully established. In solvent vapor annealing a thin polymer film is exposed to the vapors of a solvent(s) thus forming a swollen and mobile layer to direct the self-assembly process at the nanoscale. Recent developments in both theory and experiment have directly identified critical parameters, but controlling them in any systematic way has proven non-trivial. These identified parameters include vapor pressure, solvent concentration in the film, and, critically, the solvent evaporation rate. To explore their role, a purpose-built solvent vapor annealing chamber was designed and constructed. The all-metal chamber is inert to solvent exposure and pneumatically actuated valves allow for precision timing in the introduction and withdrawal of solvent vapor. Furthermore, the mass flow controlled inlet, chamber pressure gauges, in situ spectral reflectance-based thickness monitoring, and high precision micrometer relief valve, give real-time monitoring and control during the annealing and evaporation phases. Using atomic force microscopy to image the annealed films, we are able to map out the parameter space for a series of polystyrene- b-polylactide (Mn = 75 kg/mol and fPLA = 0.28) block polymer thin films with an intrinsic cylindrical morphology and identify their role in directed assembly. Funded by Creighton University Summer Research Grant.

In situ grazing incidence small-angle X-ray scattering investigation of polystyrene nanoparticle spray deposition onto silicon.

PubMed

Herzog, Gerd; Benecke, Gunthard; Buffet, Adeline; Heidmann, Berit; Perlich, Jan; Risch, Johannes F H; Santoro, Gonzalo; Schwartzkopf, Matthias; Yu, Shun; Wurth, Wilfried; Roth, Stephan V

2013-09-10

We investigated the spray deposition and subsequent self-assembly during drying of a polystyrene nanoparticle dispersion with in situ grazing incidence small-angle X-ray scattering at high time resolution. During the fast deposition of the dispersion and the subsequent evaporation of the solvent, different transient stages of nanoparticle assembly can be identified. In the first stage, the solvent starts to evaporate without ordering of the nanoparticles. During the second stage, large-scale structures imposed by the breakup of the liquid film are observable. In this stage, the solvent evaporates further and nanoparticle ordering starts. In the late third drying stage, the nanoparticles self-assemble into the final layer structure.

Directed assembly of three-dimensional structures with micron-scale features

DOEpatents

Gratson, Gregory; Lewis, Jennifer A.

2006-11-28

The invention provides polyelectrolyte inks comprising a solvent, a cationic polyelectrolyte, dissolved in the solvent, and an anionic polyelectrolyte, dissolved in the solvent. The concentration of at least one of the polyelectrolytes in the solvent is in a semidilute regime.

Self-Assembly of a Strong Polyhedral Oligomeric Silsesquioxane Core-Based Aspartate Derivative Dendrimer Supramolecular Gelator in Different Polarity Solvents.

PubMed

He, Huiwen; Chen, Si; Tong, Xiaoqian; An, Zhihang; Ma, Meng; Wang, Xiaosong; Wang, Xu

2017-11-21

Aromatic groups are introduced into the end peripherals of polyhedral oligomeric silsesquioxane (POSS) core-based organic/inorganic hybrid supramolecules to get a novel dendrimer gelator POSS-Z-Asp(OBzl) (POSS-ASP), which have eight aspartate derivative arms to make full use of strong π-π stacking forces to get strong supramolecular gels in addition to multiple hydrogen bindings and van der Waals interactions. POSS-ASP can self-assemble into three-dimensional nanoscale gel networks to provide hybrid physical gels especially with strong mechanical properties and fast-recovery behaviors. Two totally different morphologies of the connected spherical particle structures and banded ultralong fibers are observed owing to the polarity of solvents confirmed by the scanning electron microscopy, polarized optical microscopy, and transmission electron microscopy techniques, expecting the existing various self-assembly models and illustrating the peripherals of the dendrimer and the polarity of solvents having huge influences in the supramolecular self-assembly mechanism. What is more, the thermal stability, rheological properties, and network architecture information have also been investigated via tube-inversion, rotational rheometer, and powder X-ray diffraction methods, the results of which confirm the two different gel formation mechanisms that make POSS-ASP to exhibit two totally different thermal and mechanical properties. Such a study reports a new gelation system in organic or organic/aqueous mixed solvents, which can be helpful for investigating the relationship of dendritic supramolecular gelation and different polarity solvents during the supramolecular self-assembly process of gelators.

Self-Assembly and Nanostructures in Organogels Based on a Bolaform Cholesteryl Imide Compound with Conjugated Aromatic Spacer

PubMed Central

Jiao, Ti-Feng; Gao, Feng-Qing; Shen, Xi-Hai; Zhang, Qing-Rui; Zhang, Xian-Fu; Zhou, Jing-Xin; Gao, Fa-Ming

2013-01-01

The self-assembly of small functional molecules into supramolecular structures is a powerful approach toward the development of new nanoscale materials and devices. As a class of self-assembled materials, low weight molecular organic gelators, organized in special nanoarchitectures through specific non-covalent interactions, has become one of the hot topics in soft matter research due to their scientific values and many potential applications. Here, a bolaform cholesteryl imide compound with conjugated aromatic spacer was designed and synthesized. The gelation behaviors in 23 solvents were investigated as efficient low-molecular-mass organic gelator. The experimental results indicated that the morphologies and assembly modes of as-formed organogels can be regulated by changing the kinds of organic solvents. Scanning electron microscopy and atomic force microscopy observations revealed that the gelator molecule self-assemble into different aggregates, from wrinkle and belt to fiber with the change of solvents. Spectral studies indicated that there existed different H-bond formations between imide groups and assembly modes. Finally, some rational assembly modes in organogels were proposed and discussed. The present work may give some insight to the design and character of new organogelators and soft materials with special structures. PMID:28788428

3D investigation on polystyrene colloidal crystals by floatage self-assembly with mixed solvent via synchrotron radiation x-ray phase-contrast computed tomography

NASA Astrophysics Data System (ADS)

Fu, Yanan; Xie, Honglan; Deng, Biao; Du, Guohao; Xiao, Tiqiao

2017-06-01

The floatage self-assembly method was introduced with mixed solvent as the medium of polystyrene sphere suspension to fabricate the colloidal crystal. The three dimensional (3D) void system of the colloidal crystal was noninvasively characterized by synchrotron radiation phase-contrast computed tomography, and the quantitative image analysis was implemented aiming to the polystyrene sphere colloidal crystal. Comparing with gravity sedimentation method, the three samples fabricated from floatage self-assembly with mixed solvents have the lowest porosity, and when ethylene glycol and water were mixed with ratio of 1:1, the lowest porosity of 27.49% could be achieved, that has been very close to the minimum porosity of ordered 3D monodisperse sphere array (26%). In single slices, the porosities and fractal dimension for the voids were calculated. The results showed that two factors would significantly influence the porosity of the whole colloidal crystal: the first deposited sphere layer's orderliness and the sedimentation speed of the spheres. The floatage self-assembly could induce a stable close-packing process, resulted from the powerful nucleation force-lateral capillary force coupled with the mixed solvent to regulate the floating upward speed for purpose of matching the assembly rate.

Block copolymer systems: from single chain to self-assembled nanostructures.

PubMed

Giacomelli, Cristiano; Schmidt, Vanessa; Aissou, Karim; Borsali, Redouane

2010-10-19

Recent advances in the field of macromolecular engineering applied to the fabrication of nanostructured materials using block copolymer chains as elementary building blocks are described in this feature article. By highlighting some of our work in the area and accounting for the contribution of other groups, we discuss the relationship between the physical-chemical properties of copolymer chains and the characteristics of nano-objects originating from their self-assembly in solution and in bulk, with emphasis on convenient strategies that allow for the control of composition, functionality, and topology at different levels of sophistication. In the case of micellar nanoparticles in solution, in particular, we present approaches leading to morphology selection via macromolecular architectural design, the functionalization of external solvent-philic shells with biomolecules (polysaccharides and proteins), and the maximization of micelle loading capacity by the suitable choice of solvent-phobic polymer segments. The fabrication of nanomaterials mediated by thin block copolymer films is also discussed. In this case, we emphasize the development of novel polymer chain manipulation strategies that ultimately allow for the preparation of precisely positioned nanodomains with a reduced number of defects via block-selective chemical reactivity. The challenges facing the soft matter community, the urgent demand to convert huge public and private investments into consumer products, and future possible directions in the field are also considered herein.

Self-assembly of star micelle into vesicle in solvents of variable quality: the star micelle retains its core-shell nanostructure in the vesicle.

PubMed

Liu, Nijuan; He, Qun; Bu, Weifeng

2015-03-03

Intra- and intermolecular interactions of star polymers in dilute solutions are of fundamental importance for both theoretical interest and hierarchical self-assembly into functional nanostructures. Here, star micelles with a polystyrene corona and a small ionic core bearing platinum(II) complexes have been regarded as a model of star polymers to mimic their intra- and interstar interactions and self-assembled behaviors in solvents of weakening quality. In the chloroform/methanol mixture solvents, the star micelles can self-assemble to form vesicles, in which the star micelles shrink significantly and are homogeneously distributed on the vesicle surface. Unlike the morphological evolution of conventional amphiphiles from micellar to vesicular, during which the amphiphilic molecules are commonly reorganized, the star micelles still retain their core-shell nanostructures in the vesicles and the coronal chains of the star micelle between the ionic cores are fully interpenetrated.

Surface mediated assembly of small, metastable gold nanoclusters

NASA Astrophysics Data System (ADS)

Pettibone, John M.; Osborn, William A.; Rykaczewski, Konrad; Talin, A. Alec; Bonevich, John E.; Hudgens, Jeffrey W.; Allendorf, Mark D.

2013-06-01

The unique properties of metallic nanoclusters are attractive for numerous commercial and industrial applications but are generally less stable than nanocrystals. Thus, developing methodologies for stabilizing nanoclusters and retaining their enhanced functionality is of great interest. We report the assembly of PPh3-protected Au9 clusters from a heterogeneous mixture into films consisting of sub 3 nm nanocluster assemblies. The depositing nanoclusters are metastable in solution, but the resulting nanocluster assemblies are stabilized indefinitely in air or fresh solvent. The films exhibit distinct structure from Au nanoparticles observed by X-ray diffraction, and film dissolution data support the preservation of small nanoclusters. UV-Vis spectroscopy, electrospray ionization mass spectrometry, X-ray photoelectron spectroscopy and electron microscopy are used to elucidate information regarding the nanocluster formation and assembly mechanism. Preferential deposition of nanocluster assemblies can be achieved on multiple substrates, including polymer, Cr, Si, SiO2, SiNx, and metal-organic frameworks (MOFs). Unlike other vapor phase coating processes, nanocluster assembly on the MIL-68(In) MOF crystal is capable of preferentially coating the external surface and stabilizing the crystal structure in hydrothermal conditions, which should enhance their storage, separation and delivery capabilities.The unique properties of metallic nanoclusters are attractive for numerous commercial and industrial applications but are generally less stable than nanocrystals. Thus, developing methodologies for stabilizing nanoclusters and retaining their enhanced functionality is of great interest. We report the assembly of PPh3-protected Au9 clusters from a heterogeneous mixture into films consisting of sub 3 nm nanocluster assemblies. The depositing nanoclusters are metastable in solution, but the resulting nanocluster assemblies are stabilized indefinitely in air or fresh solvent. The films exhibit distinct structure from Au nanoparticles observed by X-ray diffraction, and film dissolution data support the preservation of small nanoclusters. UV-Vis spectroscopy, electrospray ionization mass spectrometry, X-ray photoelectron spectroscopy and electron microscopy are used to elucidate information regarding the nanocluster formation and assembly mechanism. Preferential deposition of nanocluster assemblies can be achieved on multiple substrates, including polymer, Cr, Si, SiO2, SiNx, and metal-organic frameworks (MOFs). Unlike other vapor phase coating processes, nanocluster assembly on the MIL-68(In) MOF crystal is capable of preferentially coating the external surface and stabilizing the crystal structure in hydrothermal conditions, which should enhance their storage, separation and delivery capabilities. Electronic supplementary information (ESI) available: Further details on stored plating solution preparation, film characterization, solution processing, MOF crystal FIB reconstruction and stability are available. See DOI: 10.1039/c3nr01708g

Water-induced nanochannel networks in self-assembled block ionomers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mineart, Kenneth P.; Al-Mohsin, Heba A.; Lee, Byeongdu

2016-03-07

Block ionomers cast from solution exhibit solvent-templated morphologies that can be altered by solvent-vapor annealing. When cast from a mixed solvent, a midblock-sulfonated pentablock ion- omer self-assembles into spherical ionic microdomains that are loosely connected. Upon exposure to liquid water, nanoscale channels irreversibly develop between the microdomains due to swelling and form a continuous mesoscale network. We use electron tomography and real-time X-ray scat- tering to follow this transformation and show that the resultant morphology provides a highly effec- tive diffusive pathway.

Induced-Dipole-Directed, Cooperative Self-Assembly of a Benzotrithiophene.

PubMed

Ikeda, Toshiaki; Adachi, Hiroaki; Fueno, Hiroyuki; Tanaka, Kazuyoshi; Haino, Takeharu

2017-10-06

A benzotrithiophene derivative possessing phenylisoxazoles self-assembled to form stacks. The molecule isodesmically self-assembled in chloroform, whereas it self-assembled in a cooperative fashion in decalin and in methylcyclohexane. Thermodynamic studies based on isodesmic, van der Schoot, and Goldstein-Stryer mathematical models revealed that the self-assembly processes are enthalpically driven and entropically opposed. An enthalpy-entropy compensation plot indicates that the assembly processes in chloroform, decalin, and methylcyclohexane are closely related. The enthalpic gains in less-polar solvents are greater than those in more-polar solvents, resulting in the formation of large assemblies in decalin and in methylcyclohexane. The formation of large assemblies leads to cooperative assemblies. The elongation process is enthalpically more favored than the nucleation process, which drives the cooperativity of the self-assembly. DFT calculations suggested that a hexameric assembly is more stable than tetrameric or dimeric assemblies. Cooperative self-assemblies based on intermolecular interactions other than hydrogen bonding have rarely been reported. It is demonstrated herein that van der Waals interactions, including induced dipole-dipole interactions, can drive the cooperative assembly of planar π-conjugated molecules.

Gold nanoparticle capture within protein crystal scaffolds.

PubMed

Kowalski, Ann E; Huber, Thaddaus R; Ni, Thomas W; Hartje, Luke F; Appel, Karina L; Yost, Jarad W; Ackerson, Christopher J; Snow, Christopher D

2016-07-07

DNA assemblies have been used to organize inorganic nanoparticles into 3D arrays, with emergent properties arising as a result of nanoparticle spacing and geometry. We report here the use of engineered protein crystals as an alternative approach to biologically mediated assembly of inorganic nanoparticles. The protein crystal's 13 nm diameter pores result in an 80% solvent content and display hexahistidine sequences on their interior. The hexahistidine sequence captures Au25(glutathione)∼17 (nitrilotriacetic acid)∼1 nanoclusters throughout a chemically crosslinked crystal via the coordination of Ni(ii) to both the cluster and the protein. Nanoparticle loading was validated by confocal microscopy and elemental analysis. The nanoparticles may be released from the crystal by exposure to EDTA, which chelates the Ni(ii) and breaks the specific protein/nanoparticle interaction. The integrity of the protein crystals after crosslinking and nanoparticle capture was confirmed by single crystal X-ray crystallography.

Solvent polarity effect on quality of n-octadecanethiol self-assembled monolayers on copper and oxidized copper

NASA Astrophysics Data System (ADS)

Zhang, Yaozhong; Zhou, Jun; Zhang, Xiaoli; Hu, Jun; Gao, Han

2014-11-01

This article reports the effect of solvent polarity on the formation of n-octadecanethiol self-assembled monolayers (C18SH-SAMs) on pure copper surface and oxidized copper surface. The quality of SAMs prepared in different solvents (n-hexane, toluene, trichloroethylene, chloroform, acetone, acetonitrile, ethanol) was monitored by EIS, RAIRS and XPS. The results indicated that C18SH-SAMs formed in these solvents were in good barrier properties on pure copper surface and the structures of monolayers formed in high polarity solvents were more compact and orderly than that formed in low polarity solvents. For comparison, C18SH adsorbed on the surface of oxidized copper in these solvents were studied and the results indicated that C18SH could be adsorbed on oxidized copper surface after the reduction of copper oxide layer by thiols. Compared with high polarity solvents, a limited reduction process of oxidized copper by thiols led to the incompletely formation of monolayers in low polarity solvents. This can be interpreted that the generated water on solid-liquid interface and a smaller reaction force restrict the continuous reduction reaction in low polarity solvents

Diblock-copolymer-mediated self-assembly of protein-stabilized iron oxide nanoparticle clusters for magnetic resonance imaging.

PubMed

Tähkä, Sari; Laiho, Ari; Kostiainen, Mauri A

2014-03-03

Superparamagnetic iron oxide nanoparticles (SPIONs) can be used as efficient transverse relaxivity (T2 ) contrast agents in magnetic resonance imaging (MRI). Organizing small (D<10 nm) SPIONs into large assemblies can considerably enhance their relaxivity. However, this assembly process is difficult to control and can easily result in unwanted aggregation and precipitation, which might further lead to lower contrast agent performance. Herein, we present highly stable protein-polymer double-stabilized SPIONs for improving contrast in MRI. We used a cationic-neutral double hydrophilic poly(N-methyl-2-vinyl pyridinium iodide-block-poly(ethylene oxide) diblock copolymer (P2QVP-b-PEO) to mediate the self-assembly of protein-cage-encapsulated iron oxide (γ-Fe2 O3 ) nanoparticles (magnetoferritin) into stable PEO-coated clusters. This approach relies on electrostatic interactions between the cationic N-methyl-2-vinylpyridinium iodide block and magnetoferritin protein cage surface (pI≈4.5) to form a dense core, whereas the neutral ethylene oxide block provides a stabilizing biocompatible shell. Formation of the complexes was studied in aqueous solvent medium with dynamic light scattering (DLS) and cryogenic transmission electron microcopy (cryo-TEM). DLS results indicated that the hydrodynamic diameter (Dh ) of the clusters is approximately 200 nm, and cryo-TEM showed that the clusters have an anisotropic stringlike morphology. MRI studies showed that in the clusters the longitudinal relaxivity (r1 ) is decreased and the transverse relaxivity (r2 ) is increased relative to free magnetoferritin (MF), thus indicating that clusters can provide considerable contrast enhancement. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Spacer effect on nanostructures and self-assembly in organogels via some bolaform cholesteryl imide derivatives with different spacers

PubMed Central

2013-01-01

In this paper, new bolaform cholesteryl imide derivatives with different spacers were designed and synthesized. Their gelation behaviors in 23 solvents were investigated, and some of them were found to be low molecular mass organic gelators. The experimental results indicated that these as-formed organogels can be regulated by changing the flexible/rigid segments in spacers and organic solvents. Suitable combination of flexible/rigid segments in molecular spacers in the present cholesteryl gelators is favorable for the gelation of organic solvents. Scanning electron microscopy and atomic force microscopy observations revealed that the gelator molecules self-assemble into different aggregates, from wrinkle and belt to fiber with the change of spacers and solvents. Spectral studies indicated that there existed different H-bond formations between imide groups and assembly modes, depending on the substituent spacers in molecular skeletons. The present work may give some insight into the design and character of new organogelators and soft materials with special molecular structures. PMID:24083361

Spacer effect on nanostructures and self-assembly in organogels via some bolaform cholesteryl imide derivatives with different spacers

NASA Astrophysics Data System (ADS)

Jiao, Tifeng; Gao, Fengqing; Zhang, Qingrui; Zhou, Jingxin; Gao, Faming

2013-10-01

In this paper, new bolaform cholesteryl imide derivatives with different spacers were designed and synthesized. Their gelation behaviors in 23 solvents were investigated, and some of them were found to be low molecular mass organic gelators. The experimental results indicated that these as-formed organogels can be regulated by changing the flexible/rigid segments in spacers and organic solvents. Suitable combination of flexible/rigid segments in molecular spacers in the present cholesteryl gelators is favorable for the gelation of organic solvents. Scanning electron microscopy and atomic force microscopy observations revealed that the gelator molecules self-assemble into different aggregates, from wrinkle and belt to fiber with the change of spacers and solvents. Spectral studies indicated that there existed different H-bond formations between imide groups and assembly modes, depending on the substituent spacers in molecular skeletons. The present work may give some insight into the design and character of new organogelators and soft materials with special molecular structures.

Surface Patterning of Benzene Carboxylic Acids on Graphite: Influence of structure, solvent, and concentration on molecular self-assembly

NASA Astrophysics Data System (ADS)

Florio, Gina; Stiso, Kimberly; Campanelli, Joseph; Dessources, Kimberly; Folkes, Trudi

2012-02-01

Scanning tunneling microscopy (STM) was used to investigate the molecular self-assembly of four different benzene carboxylic acid derivatives at the liquid/graphite interface: pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), trimellitic acid (1,2,4-benzenetricarboxylic acid), trimesic acid (1,3,5-benzenetricarboxylic acid), and 1,3,5-benzenetriacetic acid. A range of two dimensional networks are observed that depend sensitively on the number of carboxylic acids present, the nature of the solvent, and the solution concentration. We will describe our recent efforts to determine (a) the preferential two-dimensional structure(s) for each benzene carboxylic acid at the liquid/graphite interface, (b) the thermodynamic and kinetic factors influencing self-assembly (or lack thereof), (c) the role solvent plays in the assembly, (e) the effect of in situ versus ex situ dilution on surface packing density, and (f) the temporal evolution of the self-assembled monolayer. Results of computational analysis of analog molecules and model monolayer films will also be presented to aid assignment of network structures and to provide a qualitative picture of surface adsorption and network formation.

Diversity and Hierarchy in Supramolecular Assemblies of Triphenylalanine: From Laminated Helical Ribbons to Toroids.

PubMed

Mayans, Enric; Casanovas, Jordi; Gil, Ana M; Jiménez, Ana I; Cativiela, Carlos; Puiggalí, Jordi; Alemán, Carlos

2017-04-25

Microstructures from small phenylalanine-based peptides have attracted great attention lately because these compounds are considered to be a new class of tunable materials. In spite of the extensive studies on uncapped diphenylalanine and tetraphenylalanine peptides, studies on the self-assembly of uncapped triphenylananine (FFF) are very scarce and nonsystematic. In this work, we demonstrate that FFF assemblies can organize in a wide number of well-defined supramolecular structures, which include laminated helical-ribbons, leaflike dendrimers, doughnut-, needle-, and flower-shapes. These organizations are produced by the attractive or repulsive interactions between already formed assemblies and therefore can be controlled through the choice of solvents used as the incubation medium. Thus, the formation of the desired supramolecular structures is regulated through the protonation/deprotonation of the terminal groups, the polarity of the incubation medium, which affects both peptide···solvent interactions and the cavity solvation energy (i.e., solvent···solvent interactions), and the steric interactions between own assemblies that act as building blocks. Finally, the β-sheet disposition in the latter structural motifs has been examined using both theoretical calculations and Fourier transform infrared spectroscopy. Results indicate that FFF molecules can adopt both parallel and antiparallel β-sheets. However, the former one is the most energetically favored because of the formation of π-π stacking interactions between the aromatic rings of hydrogen-bonded strands.

Dewetting-mediated pattern formation in nanoparticle assemblies

NASA Astrophysics Data System (ADS)

Stannard, Andrew

2011-03-01

The deposition of nanoparticles from solution onto solid substrates is a diverse subfield of current nanoscience research. Complex physical and chemical processes underpin the self-assembly and self-organization of colloidal nanoparticles at two-phase (solid-liquid, liquid-air) interfaces and three-phase (solid-liquid-air) contact lines. This review discusses key recent advances made in the understanding of nonequilibrium dewetting processes of nanoparticle-containing solutions, detailing how such an apparently simple experimental system can give rise to such a strikingly varied palette of two-dimensional self-organized nanoparticle array morphologies. Patterns discussed include worm-like domains, cellular networks, microscale rings, and fractal-like fingering structures. There remain many unresolved issues regarding the role of the solvent dewetting dynamics in assembly processes of this type, with a significant focus on how dewetting can be coerced to produce nanoparticle arrays with desirable characteristics such as long-range order. In addition to these topics, methods developed to control nanofluid dewetting through routes such as confining the geometries of drying solutions, depositing onto pre-patterned heterogeneous substrates, and post-dewetting pattern evolution via local or global manipulation are covered.

Dewetting-mediated pattern formation in nanoparticle assemblies.

PubMed

Stannard, Andrew

2011-03-02

The deposition of nanoparticles from solution onto solid substrates is a diverse subfield of current nanoscience research. Complex physical and chemical processes underpin the self-assembly and self-organization of colloidal nanoparticles at two-phase (solid-liquid, liquid-air) interfaces and three-phase (solid-liquid-air) contact lines. This review discusses key recent advances made in the understanding of nonequilibrium dewetting processes of nanoparticle-containing solutions, detailing how such an apparently simple experimental system can give rise to such a strikingly varied palette of two-dimensional self-organized nanoparticle array morphologies. Patterns discussed include worm-like domains, cellular networks, microscale rings, and fractal-like fingering structures. There remain many unresolved issues regarding the role of the solvent dewetting dynamics in assembly processes of this type, with a significant focus on how dewetting can be coerced to produce nanoparticle arrays with desirable characteristics such as long-range order. In addition to these topics, methods developed to control nanofluid dewetting through routes such as confining the geometries of drying solutions, depositing onto pre-patterned heterogeneous substrates, and post-dewetting pattern evolution via local or global manipulation are covered.

Molecular insights into early stage aggregation of di-Fmoc-L-lysine in binary mixture of organic solvent and water

NASA Astrophysics Data System (ADS)

Huda, Md Masrul; Rai, Neeraj

Molecular gels are relatively new class of soft materials, which are formed by the supramolecular aggregation of low molecular weight gelators (LMWGs) in organic solvents and/or water. Hierarchical self-assembly of small gelator molecules lead to three-dimensional complex fibrillar networks, which restricts the flow of solvents and results in viscous solid like materials or gels. These gels have drawn significant attentions for their potential applications for drug delivery, tissue engineering, materials for sensors etc. As of now, self-assembly of gelator molecules into one-dimensional fibers is not well understood, although that is very important to design new gelators for desired applications. Here, we present molecular dynamics study that provides molecular level insight into early stage aggregation of selected gelator, di-Fmoc-L-lysine in binary mixture of organic solvent and water. We will present the role of different functional groups of gelator molecule such as aromatic ring, amide, and carboxylic group on aggregation. We will also present the effect of concentrations of gelator and solvent on self-assembly of gelators. This study has captured helical fiber growth and branching of fiber, which is in good agreement with experimental observations.

Temperature-dependent self-assembly and rheological behavior of a thermoreversible pmma-P n BA-PMMA triblock copolymer gel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zabet, Mahla; Mishra, Satish; Boy, Ramiz

Self-assembly and mechanical properties of triblock copolymers in a mid-block selective solvent are of interest in many applications. Herein, we report physical assembly of an ABA triblock copolymer, [PMMA–PnBA–PMMA] in two different mid-block selective solvents, n-butanol and 2-ethyl-1-hexanol. Gel formation resulting from end-block associations and the corresponding changes in mechanical properties have been investigated over a temperature range of -80 °C to 60 °C, from near the solvent melting points to above the gelation temperature. Shear-rheometry, thermal analysis, and small-angle neutron scattering data reveal formation and transition of structure in these systems from a liquid state to a gel statemore » to a percolated cluster network with decrease in temperature. The aggregated PMMA end-blocks display a glass transition temperature. Our results provide new understanding into the structural changes of a self-assembled triblock copolymer gel over a large length scale and wide temperature range.« less

Structure, morphology, and assembly behavior of kafirin

DOE PAGES

Xiao, Jie; Li, Yunqi; Li, Ji; ...

2014-12-15

Prolamins from grains have attracted intensive attention in recent years due to their potential in satisfying the demand for environmentally friendly (biodegradable), abundantly available (sustainable), and cost-effective biomaterials. However, for kafirin, the prolamin from sorghum, its composition, structure, morphology, and self-assembly behaviors have not been fully characterized. In this paper, kafirin was extracted from the whole sorghum grain and found to contain 68, 14, 6, and 12% of α-, β-, and γ-fractions and cross-linked kafirin, respectively. Freeze-dried kafirin contained ~49% α-helix in the solid state. When dissolved in 65% (v/v) isopropanol, 60% (v/v) tert-butanol, and 85% (v/v) ethanol aqueous solvents,more » the relative α-helix content in kafirin increased with the decrease of solvent polarity. Structural analysis using small-angle X-ray scattering (SAXS) indicated that kafirin (2 mg/mL) took stretched and extended conformations with dimensions of 118 × 15 × 15 and 100 × 11 × 11 Å in 60% tert-butanol and 65% isopropanol, respectively. More elongated conformation of individual kafirin with high-order assembly was observed in 85% ethanol. Protein aggregation occurred as protein concentration increased in its good solvent. The morphology of kafirin assemblies captured by atomic force microscopy (AFM) revealed that kafirin protein took uniform particle morphology at low concentration, and disk-like or rod-like structures resulting from solvent evaporation induced particle interactions emerged at high concentrations. Lastly, these results suggest that both protein concentration and solvent polarity can effectively regulate kafirin assemblies from thick rod-like to slim rod-like structures, a convenient way to tune the fibrillation of prolamin-based biomaterials.« less

Advanced membrane electrode assemblies for fuel cells

DOEpatents

Kim, Yu Seung; Pivovar, Bryan S.

2012-07-24

A method of preparing advanced membrane electrode assemblies (MEA) for use in fuel cells. A base polymer is selected for a base membrane. An electrode composition is selected to optimize properties exhibited by the membrane electrode assembly based on the selection of the base polymer. A property-tuning coating layer composition is selected based on compatibility with the base polymer and the electrode composition. A solvent is selected based on the interaction of the solvent with the base polymer and the property-tuning coating layer composition. The MEA is assembled by preparing the base membrane and then applying the property-tuning coating layer to form a composite membrane. Finally, a catalyst is applied to the composite membrane.

Advanced membrane electrode assemblies for fuel cells

DOEpatents

Kim, Yu Seung; Pivovar, Bryan S

2014-02-25

A method of preparing advanced membrane electrode assemblies (MEA) for use in fuel cells. A base polymer is selected for a base membrane. An electrode composition is selected to optimize properties exhibited by the membrane electrode assembly based on the selection of the base polymer. A property-tuning coating layer composition is selected based on compatibility with the base polymer and the electrode composition. A solvent is selected based on the interaction of the solvent with the base polymer and the property-tuning coating layer composition. The MEA is assembled by preparing the base membrane and then applying the property-tuning coating layer to form a composite membrane. Finally, a catalyst is applied to the composite membrane.

Micelle structure in a deep eutectic solvent: a small-angle scattering study.

PubMed

Sanchez-Fernandez, A; Edler, K J; Arnold, T; Heenan, R K; Porcar, L; Terrill, N J; Terry, A E; Jackson, A J

2016-05-18

In recent years many studies into green solvents have been undertaken and deep eutectic solvents (DES) have emerged as sustainable and green alternatives to conventional solvents since they may be formed from cheap non-toxic organic precursors. In this study we examine amphiphile behaviour in these novel media to test our understanding of amphiphile self-assembly within environments that have an intermediate polarity between polar and non-polar extremes. We have built on our recently published results to present a more detailed structural characterisation of micelles of sodium dodecylsulfate (SDS) within the eutectic mixture of choline chloride and urea. Here we show that SDS adopts an unusual cylindrical aggregate morphology, unlike that seen in water and other polar solvents. A new morphology transition to shorter aggregates was found with increasing concentration. The self-assembly of SDS was also investigated in the presence of water; which promotes the formation of shorter aggregates.

Tunable and rapid self-assembly of block copolymers using mixed solvent vapors.

PubMed

Park, Woon Ik; Tong, Sheng; Liu, Yuzi; Jung, Il Woong; Roelofs, Andreas; Hong, Seungbum

2014-12-21

Pattern generation of well-controlled block copolymers (BCPs) with a high Flory-Huggins interaction parameter (χ) is important for applications in sub-20 nm nanolithography. We used mixed solvents of dimethylformamide (DMF) and toluene to control the morphology as well as the time to achieve the targeted morphology via self-assembly of BCPs. By precisely controlling the volume ratio of DMF and toluene, well-ordered line, honeycomb, circular hole, and lamellar nanostructures were obtained from a cylinder-forming poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) BCP with high χ. Furthermore, a well-aligned 12 nm line pattern was successfully achieved in the guiding template within one minute using the mixed solvents. This practical method may also be applicable to self-assembly of other BCPs, providing more opportunities for the next-generation sub-10 nm lithography applications.

Selectivity and Sensitivity of Ultrathin Monolayer Electrodes

NASA Astrophysics Data System (ADS)

Cheng, Quan

The objective of this work is to build a molecular architecture on the electrode surface with a well-defined morphology and desirable electrochemical characteristics. The goal is accomplished by means of self-assembly of thioctic acid, a sulfur-terminated organic molecule with a short alkyl chain and a hydrophilic carboxylic headgroup, on a gold electrode. Characterization of the monolayer structure and the electrochemical response of the monolayer electrodes is performed by means of capacitance measurements and voltammetry. Investigation of the capacitance of the self-assembled monolayers provides insight into the macroscopic permeability of the films and reveals that penetration of solvent/ions into the thioctic acid monolayer film occurs extensively. Voltammetric results demonstrate that permselectivity of the monolayer electrode can be obtained as a result of the induced electrostatic interactions between the monolayer interface and the electroactive species. Measurement of the voltammetric response of the redox probes at the monolayers as a function of the electrolyte concentration and composition is used to qualitatively analyze the effect of electrolyte on response. A model describing the role of the interfacial charge in the electrochemical response of the monolayers as a function of the solution composition and surface smoothness is proposed. A strategy is developed to further explore the applications of the monolayer electrodes to control the electrochemical response of the biological molecules such as catecholamines. The ability to control the surface hydrophobicity of the monolayer electrodes through coadsorption of thioctic acid and hexanethiol, to display different electrochemical properties towards biological molecules is tested. The optimum conditions for detection of the biological molecules on the monolayer electrodes are discussed. In order to pursue selective analysis in microenvironments, the thioctic acid monolayer formed on the ultramicroelectrodes (UME) is investigated, demonstrating high permselectivity and high sensitivity of the monolayer modified UMEs. Because of the more effective mass transport to the UMEs, effects of electrolyte on the monolayer response can be characterized facilely. Amperometric pH sensing on the thioctic acid UMEs using a redox mediator is discussed. Finally, the thioctic acid monolayer microelectrode is applied to investigate direct electrochemistry of a redox protein, cytochrome c. A sketch for developing a biosensor via mediation effects using the monolayer assembly is proposed.

DNA-mediated nanoparticle crystallization into Wulff polyhedra

NASA Astrophysics Data System (ADS)

Auyeung, Evelyn; Li, Ting I. N. G.; Senesi, Andrew J.; Schmucker, Abrin L.; Pals, Bridget C.; de La Cruz, Monica Olvera; Mirkin, Chad A.

2014-01-01

Crystallization is a fundamental and ubiquitous process much studied over the centuries. But although the crystallization of atoms is fairly well understood, it remains challenging to predict reliably the outcome of molecular crystallization processes that are complicated by various molecular interactions and solvent involvement. This difficulty also applies to nanoparticles: high-quality three-dimensional crystals are mostly produced using drying and sedimentation techniques that are often impossible to rationalize and control to give a desired crystal symmetry, lattice spacing and habit (crystal shape). In principle, DNA-mediated assembly of nanoparticles offers an ideal opportunity for studying nanoparticle crystallization: a well-defined set of rules have been developed to target desired lattice symmetries and lattice constants, and the occurrence of features such as grain boundaries and twinning in DNA superlattices and traditional crystals comprised of molecular or atomic building blocks suggests that similar principles govern their crystallization. But the presence of charged biomolecules, interparticle spacings of tens of nanometres, and the realization so far of only polycrystalline DNA-interconnected nanoparticle superlattices, all suggest that DNA-guided crystallization may differ from traditional crystal growth. Here we show that very slow cooling, over several days, of solutions of complementary-DNA-modified nanoparticles through the melting temperature of the system gives the thermodynamic product with a specific and uniform crystal habit. We find that our nanoparticle assemblies have the Wulff equilibrium crystal structure that is predicted from theoretical considerations and molecular dynamics simulations, thus establishing that DNA hybridization can direct nanoparticle assembly along a pathway that mimics atomic crystallization.

C60 Cheese Sticks: Supramolecular Architecture of an Amphiphilic Fullerene Pentapod.

PubMed

Samal, Monica; Acharya, Sandhyarani; Yi, Dong Kee; Lee, Jae-Suk; Samal, Shashadhar

2015-09-01

An amphiphillic fullerene pentaphenol derivative, C60(4-HOC6H4)5H, in an aprotic solvent N-methyl-2-pyrrolidone (NMP), spontaneously self-assembles to a hitherto unknown cheese stick-like (CS) structure. This fascinating structure is observed only for C60(4-HOC6H4)5H and only in dry NMP solvent. The reason for such unique self-assembly behavior is ascribed to solvating power typical of NMP. The CS structure is observed in a narrow concentration range of the solution. This indicates that there exists between the solute and the solvent an optimal interaction condition for CS to remain stable.

Solvent-free directed patterning of a highly ordered liquid crystalline organic semiconductor via template-assisted self-assembly for organic transistors.

PubMed

Kim, Aryeon; Jang, Kwang-Suk; Kim, Jinsoo; Won, Jong Chan; Yi, Mi Hye; Kim, Hanim; Yoon, Dong Ki; Shin, Tae Joo; Lee, Myong-Hoon; Ka, Jae-Won; Kim, Yun Ho

2013-11-20

Highly ordered organic semiconductor micropatterns of the liquid-crystalline small molecule 2,7-didecylbenzothienobenzothiophene (C10 -BTBT) are fabricated using a simple method based on template-assisted self-assembly (TASA). The liquid crystallinity of C10 -BTBT allows solvent-free fabrication of high-performance printed organic field-effect transistors (OFETs). © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-Assembly of Rod-Coil Block Copolymers on Carbon Nanotubes: A Route toward Diverse Surface Nanostructures.

PubMed

Han, Yang; Cai, Chunhua; Lin, Jiaping; Gong, Shuting; Xu, Wenheng; Hu, Rui

2018-04-14

In this work, it is reported that poly(γ-benzyl-l-glutamate)-block-poly(ethylene glycol) (PBLG-b-PEG) rod-coil block copolymers (BCPs) can disperse carbon nanotubes (CNTs) in solution and form various surface nanostructures on the CNTs via solution self-assembly. In an organic solvent that dissolves the BCPs, the PBLG rod blocks adsorb on CNT surfaces, and the BCPs form conformal coatings. Then, by the introduction of water, a selective solvent for PEG blocks, the BCPs in the coatings further self-assemble into diverse surface nanostructures, such as helices (left-handed or right-handed), gyros, spheres, and rings. The morphology of the surface nanostructure can be tailored by initial organic solvent composition, preparation temperature, feeding ratio of BCPs to CNTs, degree of polymerization of PBLG blocks, and diameter of the CNTs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Temperature-dependent self-assembly and rheological behavior of a thermoreversible pmma-P n BA-PMMA triblock copolymer gel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zabet, Mahla; Mishra, Satish; Boy, Ramiz

We present that self-assembly and mechanical properties of triblock copolymers in a mid-block selective solvent are of interest in many applications. Herein, we report physical assembly of an ABA triblock copolymer, [PMMA–PnBA–PMMA] in two different mid-block selective solvents, n-butanol and 2-ethyl-1-hexanol. Gel formation resulting from end-block associations and the corresponding changes in mechanical properties have been investigated over a temperature range of -80 °C to 60 °C, from near the solvent melting points to above the gelation temperature. Shear-rheometry, thermal analysis, and small-angle neutron scattering data reveal formation and transition of structure in these systems from a liquid state tomore » a gel state to a percolated cluster network with decrease in temperature. The aggregated PMMA end-blocks display a glass transition temperature. Finally, our results provide new understanding into the structural changes of a self-assembled triblock copolymer gel over a large length scale and wide temperature range.« less

Temperature-dependent self-assembly and rheological behavior of a thermoreversible pmma-P n BA-PMMA triblock copolymer gel

DOE PAGES

Zabet, Mahla; Mishra, Satish; Boy, Ramiz; ...

2017-03-25

We present that self-assembly and mechanical properties of triblock copolymers in a mid-block selective solvent are of interest in many applications. Herein, we report physical assembly of an ABA triblock copolymer, [PMMA–PnBA–PMMA] in two different mid-block selective solvents, n-butanol and 2-ethyl-1-hexanol. Gel formation resulting from end-block associations and the corresponding changes in mechanical properties have been investigated over a temperature range of -80 °C to 60 °C, from near the solvent melting points to above the gelation temperature. Shear-rheometry, thermal analysis, and small-angle neutron scattering data reveal formation and transition of structure in these systems from a liquid state tomore » a gel state to a percolated cluster network with decrease in temperature. The aggregated PMMA end-blocks display a glass transition temperature. Finally, our results provide new understanding into the structural changes of a self-assembled triblock copolymer gel over a large length scale and wide temperature range.« less

Advances in colloidal manipulation and transport via hydrodynamic interactions.

PubMed

Martínez-Pedrero, F; Tierno, P

2018-06-01

In this review article, we highlight many recent advances in the field of micromanipulation of colloidal particles using hydrodynamic interactions (HIs), namely solvent mediated long-range interactions. At the micrsocale, the hydrodynamic laws are time reversible and the flow becomes laminar, features that allow precise manipulation and control of colloidal matter. We focus on different strategies where externally operated microstructures generate local flow fields that induce the advection and motion of the surrounding components. In addition, we review cases where the induced flow gives rise to hydrodynamic bound states that may synchronize during the process, a phenomenon essential in different systems such as those that exhibit self-assembly and swarming. Copyright © 2018 Elsevier Inc. All rights reserved.

A microfluidic study of liquid-liquid extraction mediated by carbon dioxide.

PubMed

Lestari, Gabriella; Salari, Alinaghi; Abolhasani, Milad; Kumacheva, Eugenia

2016-07-05

Liquid-liquid extraction is an important separation and purification method; however, it faces a challenge in reducing the energy consumption and the environmental impact of solvent (extractant) recovery. The reversible chemical reactions of switchable solvents (nitrogenous bases) with carbon dioxide (CO2) can be implemented in reactive liquid-liquid extraction to significantly reduce the cost and energy requirements of solvent recovery. The development of new effective switchable solvents reacting with CO2 and the optimization of extraction conditions rely on the ability to evaluate and screen the performance of switchable solvents in extraction processes. We report a microfluidic strategy for time- and labour-efficient studies of CO2-mediated solvent extraction. The platform utilizes a liquid segment containing an aqueous extractant droplet and a droplet of a solution of a switchable solvent in a non-polar liquid, with gaseous CO2 supplied to the segment from both sides. Following the reaction of the switchable solvent with CO2, the solvent becomes hydrophilic and transfers from the non-polar solvent to the aqueous droplet. By monitoring the time-dependent variation in droplet volumes, we determined the efficiency and extraction time for the CO2-mediated extraction of different nitrogenous bases in a broad experimental parameter space. The platform enables a significant reduction in the amount of switchable solvents used in these studies, provides accurate temporal characterization of the liquid-liquid extraction process, and offers the capability of high-throughput screening of switchable solvents.

Probing the Self-Assembly and the Accompanying Structural Changes of Hydrophobin SC3 on a Hydrophobic Surface by Mass Spectrometry

PubMed Central

Wang, X.; Permentier, H. P.; Rink, R.; Kruijtzer, J. A. W.; Liskamp, R. M. J.; Wösten, H. A. B.; Poolman, B.; Robillard, G. T.

2004-01-01

The fungal class I hydrophobin SC3 self-assembles into an amphipathic membrane at hydrophilic-hydrophobic interfaces such as the water-air and water-Teflon interface. During self-assembly, the water-soluble state of SC3 proceeds via the intermediate α-helical state to the stable end form called the β-sheet state. Self-assembly of the hydrophobin at the Teflon surface is arrested in the α-helical state. The β-sheet state can be induced at elevated temperature in the presence of detergent. The structural changes of SC3 were monitored by various mass spectrometry techniques. We show that the so-called second loop of SC3 (C39–S72) has a high affinity for Teflon. Binding of this part of SC3 to Teflon was accompanied by the formation of α-helical structure and resulted in low solvent accessibility. The solvent-protected region of the second loop extended upon conversion to the β-sheet state. In contrast, the C-terminal part of SC3 became more exposed to the solvent. The results indicate that the second loop of class I hydrophobins plays a pivotal role in self-assembly at the hydrophilic-hydrophobic interface. Of interest, this loop is much smaller in case of class II hydrophobins, which may explain the differences in their assembly. PMID:15345568

Concentration-dependent multiple chirality transition in halogen-bond-driven 2D self-assembly process

NASA Astrophysics Data System (ADS)

Miao, Xinrui; Li, Jinxing; Zha, Bao; Miao, Kai; Dong, Meiqiu; Wu, Juntian; Deng, Wenli

2018-03-01

The concentration-dependent self-assembly of iodine substituted thienophenanthrene derivative (5,10-DITD) is investigated at the 1-octanic acid/graphite interface using scanning tunneling microscopy. Three kinds of chiral arrangement and transition of 2D molecular assembly mainly driven by halogen bonding is clearly revealed. At high concentration the molecules self-assembled into a honeycomb-like chiral network. Except for the interchain van der Waals forces, this pattern is stabilized by intermolecular continuous Cdbnd O⋯I⋯S halogen bonds in each zigzag line. At moderate concentration, a chiral kite-like nanoarchitecture are observed, in which the Cdbnd O⋯I⋯S and I⋯Odbnd C halogen bonds, along with the molecule-solvent Cdbnd O⋯I⋯H halogen bonds are the dominated forces to determine the structural formation. At low concentration, the molecules form a chiral cyclic network resulting from the solvent coadsorption mainly by molecule-molecule Cdbnd O⋯I⋯S halogen bonds and molecule-solvent Cdbnd O⋯I⋯H halogen bonds. The density of molecular packing becomes lower with the decreasing of the solution concentration. The solution-concentration dependent self-assembly of thienophenanthrene derivative with iodine and ester chain moieties reveals that the type of intermolecular halogen bond and the number of the co-adsorbing 1-octanic acids by molecule-solvent Cdbnd O⋯I⋯H halogen bonds determine the formation and transformation of chirality. This research emphasizes the role of different types of halogen (I) bonds in the controllable supramolecular structures and provides an approach for the fabrication of chirality.

Molecular simulations of self-assembly processes in metal-organic frameworks: Model dependence

NASA Astrophysics Data System (ADS)

Biswal, Debasmita; Kusalik, Peter G.

2017-07-01

Molecular simulation is a powerful tool for investigating microscopic behavior in various chemical systems, where the use of suitable models is critical to successfully reproduce the structural and dynamic properties of the real systems of interest. In this context, molecular dynamics simulation studies of self-assembly processes in metal-organic frameworks (MOFs), a well-known class of porous materials with interesting chemical and physical properties, are relatively challenging, where a reasonably accurate representation of metal-ligand interactions is anticipated to play an important role. In the current study, we both investigate the performance of some existing models and introduce and test new models to help explore the self-assembly in an archetypal Zn-carboxylate MOF system. To this end, the behavior of six different Zn-ion models, three solvent models, and two ligand models was examined and validated against key experimental structural parameters. To explore longer time scale ordering events during MOF self-assembly via explicit solvent simulations, it is necessary to identify a suitable combination of simplified model components representing metal ions, organic ligands, and solvent molecules. It was observed that an extended cationic dummy atom (ECDA) Zn-ion model combined with an all-atom carboxylate ligand model and a simple dipolar solvent model can reproduce characteristic experimental structures for the archetypal MOF system. The successful use of these models in extensive sets of molecular simulations, which provide key insights into the self-assembly mechanism of this archetypal MOF system occurring during the early stages of this process, has been very recently reported.

From micelle supramolecular assemblies in selective solvents to isoporous membranes.

PubMed

Nunes, Suzana P; Karunakaran, Madhavan; Pradeep, Neelakanda; Behzad, Ali Reza; Hooghan, Bobby; Sougrat, Rachid; He, Haoze; Peinemann, Klaus-Viktor

2011-08-16

The supramolecular assembly of PS-b-P4VP copolymer micelles induced by selective solvent mixtures was used to manufacture isoporous membranes. Micelle order in solution was confirmed by cryo-scanning electron microscopy in casting solutions, leading to ordered pore morphology. When dioxane, a solvent that interacts poorly with the micelle corona, was added to the solution, polymer-polymer segment contact was preferential, increasing the intermicelle contact. Immersion in water gave rise to asymmetric porous membranes with exceptional pore uniformity and high porosity. The introduction of a small number of carbon nanotubes to the casting solution improved the membrane stability and the reversibility of the gate response in the presence of different pH values.

Regulation of substituent groups on morphologies and self-assembly of organogels based on some azobenzene imide derivatives

NASA Astrophysics Data System (ADS)

Jiao, Tifeng; Wang, Yujin; Zhang, Qingrui; Zhou, Jingxin; Gao, Faming

2013-04-01

In this paper, new azobenzene imide derivatives with different substituent groups were designed and synthesized. Their gelation behaviors in 21 solvents were tested as novel low-molecular-mass organic gelators. It was shown that the alkyl substituent chains and headgroups of azobenzene residues in gelators played a crucial role in the gelation behavior of all compounds in various organic solvents. More alkyl chains in molecular skeletons in present gelators are favorable for the gelation of organic solvents. Scanning electron microscopy and atomic force microscopy observations revealed that the gelator molecules self-assemble into different aggregates, from wrinkle, lamella, and belt to fiber with the change of solvents. Spectral studies indicated that there existed different H-bond formations between amide groups and conformations of methyl chains. The present work may give some insight to the design and character of new organogelators and soft materials with special molecular structures.

Regulation of substituent groups on morphologies and self-assembly of organogels based on some azobenzene imide derivatives

PubMed Central

2013-01-01

In this paper, new azobenzene imide derivatives with different substituent groups were designed and synthesized. Their gelation behaviors in 21 solvents were tested as novel low-molecular-mass organic gelators. It was shown that the alkyl substituent chains and headgroups of azobenzene residues in gelators played a crucial role in the gelation behavior of all compounds in various organic solvents. More alkyl chains in molecular skeletons in present gelators are favorable for the gelation of organic solvents. Scanning electron microscopy and atomic force microscopy observations revealed that the gelator molecules self-assemble into different aggregates, from wrinkle, lamella, and belt to fiber with the change of solvents. Spectral studies indicated that there existed different H-bond formations between amide groups and conformations of methyl chains. The present work may give some insight to the design and character of new organogelators and soft materials with special molecular structures. PMID:23566628

Solvent-assisted self-assembly of fullerene into single-crystal ultrathin microribbons as highly sensitive UV-visible photodetectors.

PubMed

Wei, Lang; Yao, Jiannian; Fu, Hongbing

2013-09-24

The size, shape, and crystallinity of organic nanostructures play an important role in their physical properties and are mainly determined by the self-assembling kinetics of molecular components often involving the solvent conditions. Here, we reported a kinetically controlled self-assembly of C60 assisted by the solvent carbon bisulfide (CS2) into single-crystal ultrathin microribbons of 2C60·3CS2, upon mixing the poor solvent isopropyl alcohol with a C60/CS2 stock solution. Surface energy calculations reveal that these microribbons represent a kinetically favored high-energy state as compared with the thermodynamically stable shape of prismatic rods. High-resolution transmission electron microscopy observations clarify that association of CS2 at the nucleation stage helps to guide and rigidify the formation of π-π stacking 1D chains of C60 through the surrounding CS2 cage-like structures, which further act as glue, boosting lateral assembly of as-formed 1D chains into untrathin 2D microribbon single crystals. Precise control over the thickness, width, and length of 2C60·3CS2 microribbons was achieved by manipulation of the growth kinetics through adjusting the solvent conditions. Upon heating to 120 °C, sublimation of CS2 components results in fcc C60 microribbons. We found that both microribbons of solvated monoclinic 2C60·3CS2 and pure fcc C60 exhibit highly sensitive photoconductivity properties with a spectral response range covering UV to visible. The highest on/off ratio of two-terminal photodetectors based on single ribbons reaches around 250, while the responsitivity is about 75.3 A W(-1) in the UV region and 90.4 A W(-1) in the visible region.

A switchable self-assembling and disassembling chiral system based on a porphyrin-substituted phenylalanine-phenylalanine motif

NASA Astrophysics Data System (ADS)

Charalambidis, Georgios; Georgilis, Evangelos; Panda, Manas K.; Anson, Christopher E.; Powell, Annie K.; Doyle, Stephen; Moss, David; Jochum, Tobias; Horton, Peter N.; Coles, Simon J.; Linares, Mathieu; Beljonne, David; Naubron, Jean-Valère; Conradt, Jonas; Kalt, Heinz; Mitraki, Anna; Coutsolelos, Athanassios G.; Balaban, Teodor Silviu

2016-09-01

Artificial light-harvesting systems have until now not been able to self-assemble into structures with a large photon capture cross-section that upon a stimulus reversibly can switch into an inactive state. Here we describe a simple and robust FLFL-dipeptide construct to which a meso-tetraphenylporphyrin has been appended and which self-assembles to fibrils, platelets or nanospheres depending on the solvent composition. The fibrils, functioning as quenched antennas, give intense excitonic couplets in the electronic circular dichroism spectra which are mirror imaged if the unnatural FDFD-analogue is used. By slightly increasing the solvent polarity, these light-harvesting fibres disassemble to spherical structures with silent electronic circular dichroism spectra but which fluoresce. Upon further dilution with the nonpolar solvent, the intense Cotton effects are recovered, thus proving a reversible switching. A single crystal X-ray structure shows a head-to-head arrangement of porphyrins that explains both their excitonic coupling and quenched fluorescence.

Self-Assembly and Drug Release Capacities of Organogels via Some Amide Compounds with Aromatic Substituent Headgroups

PubMed Central

Zhang, Lexin; Jiao, Tifeng; Ma, Kai; Xing, Ruirui; Liu, Yamei; Xiao, Yong; Zhou, Jingxin; Zhang, Qingrui; Peng, Qiuming

2016-01-01

In this work, some amide compounds with different aromatic substituent headgroups were synthesized and their gelation self-assembly behaviors in 22 solvents were characterized as new gelators. The obtained results indicated that the size of aromatic substituent headgroups in molecular skeletons in gelators showed crucial effect in the gel formation and self-assembly behavior of all compounds in the solvents used. Larger aromatic headgroups in molecular structures in the synthesized gelator molecules are helpful to form various gel nanostructures. Morphological investigations showed that the gelator molecules can self-assembly and stack into various organized aggregates with solvent change, such as wrinkle, belt, rod, and lamella-like structures. Spectral characterizations suggested that there existed various weak interactions including π-π stacking, hydrogen bonding, and hydrophobic forces due to aromatic substituent headgroups and alkyl substituent chains in molecular structures. In addition, the drug release capacities experiments demonstrated that the drug release rate in present obtained gels can be tuned by adjusting the concentrations of dye. The present work would open up enormous insight to design and investigate new kind of soft materials with designed molecular structures and tunable drug release performance. PMID:28773663

Molecular simulations of self-assembly processes of amphiphiles in dilute solutions: the challenge for quantitative modelling

NASA Astrophysics Data System (ADS)

Jusufi, Arben

2013-11-01

We report on two recent developments in molecular simulations of self-assembly processes of amphiphilic solutions. We focus on the determination of micelle formation of ionic surfactants which exhibit the archetype of self-assembling compounds in solution. The first approach is centred on the challenge in predicting micellisation properties through explicit solvent molecular dynamics simulations. Even with a coarse-grained (CG) approach and the use of highly optimised software packages run on graphics processing unit hardware, it remains in many cases computationally infeasible to directly extract the critical micelle concentration (cmc). However, combined with a recently presented theoretical mean-field model this task becomes resolved. An alternative approach to study self-assembly is through implicit solvent modelling of the surfactants. Here we review some latest results and present new ones regarding capabilities of such a modelling approach in determining the cmc, and the aggregate structures in the dilute regime, that is currently not accessible through explicit solvent simulations, neither through atomistic nor through CG approaches. A special focus is put on surfactant concentration effects and surfactant correlations quantified by scattering intensities that are compared to recently published small-angle X-ray scattering data.

MICROWAVE-FACILITATED MULTICOMPONENT REACTIONS UNDER SOLVENT-FREE CONDITIONS

EPA Science Inventory

The application of microwave-expedited solvent-free synthetic protocols in multi-component (MCC) reactions will be exemplified by several condensation and cyclization reactions including the rapid one-pot assembly of heterocyclic compounds from in situ generated intermediates. R...

Tuning Structural Properties of Biocompatible Block Copolymer Micelles by Varying Solvent Composition

NASA Astrophysics Data System (ADS)

Cooksey, Tyler; Singh, Avantika; Mai Le, Kim; Wang, Shu; Kelley, Elizabeth; He, Lilin; Vajjala Kesava, Sameer; Gomez, Enrique; Kidd, Bryce; Madsen, Louis; Robertson, Megan

The self-assembly of block copolymers into micelles when introduced to selective solvents enables a wide array of applications, ranging from drug delivery to personal care products to nanoreactors. In order to probe the assembly and dynamics of micellar systems, the structural properties and solvent uptake of biocompatible poly(ethylene oxide-b- ɛ-caprolactone) (PEO-PCL) diblock copolymers in deuterated water (D2O) / tetrahydrofuran (THFd8) mixtures were investigated using small-angle neutron scattering in combination with nuclear magnetic resonance. PEO-PCL block copolymers, of varying molecular weight yet constant block ratio, formed spherical micelles through a wide range of solvent compositions. Varying the composition from 10 to 60 % by volume THFd8\\ in D2O / THFd8 mixtures was a means of varying the core-corona interfacial tension in the micelle system. An increase in THFd8 content in the bulk solvent increased the solvent uptake within the micelle core, which was comparable for the two series, irrespective of the polymer molecular weight. Differences in the behaviors of the micelle size parameters as the solvent composition varied originated from the differing trends in aggregation number for the two micelle series. Incorporation of the known unimer content determined from NMR allowed refinement of extracted micelle parameters.

Electrostatic Interactions and Self-Assembly in Polymeric Systems

NASA Astrophysics Data System (ADS)

Dobrynin, Andrey

Electrostatic interactions between macroions play an important role in different areas ranging from materials science to biophysics. They are main driving forces behind layer-by-layer assembly technique that allows self-assembly of multilayer films from synthetic polyelectrolytes, DNA, proteins and nanoparticles. They are responsible for complexation and reversible gelation between polyelectrolytes and proteins. In this talk, using results of the molecular dynamics simulations and analytical calculations, I will demonstrate what effect electrostatic interactions, counterion condensation and polymer solvent affinity have on a collapse of polyelectrolyte chain in a poor solvent conditions for the polymer backbone, on complexations and reversible gelation between polyelectrolytes and polyamholytes (unstructured proteins), on microphase separation transitions in spherical and planar charged brushes, and on a layer-by-layer assembly of charged nanoparticles and linear polyelectrolytes on charged surfaces. NSF DMR-1004576 DMR-1409710.

Dendronization-induced phase-transfer, stabilization and self-assembly of large colloidal Au nanoparticles

NASA Astrophysics Data System (ADS)

Malassis, Ludivine; Jishkariani, Davit; Murray, Christopher B.; Donnio, Bertrand

2016-07-01

The phase-transfer of CTAB-coated aqueous, spherical gold nanoparticles, with metallic core diameters ranging from ca. 27 to 54 nm, into organic solvents by exchanging the primitive polar bilayer with lipophilic, disulfide dendritic ligands is reported. The presence of such a thick nonpolar organic shell around these large nanoparticles enhances their stabilization against aggregation, in addition to enabling their transfer into a variety of solvents such as chloroform, toluene or tetrahydrofuran. Upon the slow evaporation of a chloroform suspension deposited on a solid support, the dendronized hybrids were found to self-assemble into ring structures of various diameters. Moreover, their self-assembly at the liquid-air interface affords the formation of fairly long-range ordered monolayers, over large areas, that can then be entirely transferred onto solid substrates.The phase-transfer of CTAB-coated aqueous, spherical gold nanoparticles, with metallic core diameters ranging from ca. 27 to 54 nm, into organic solvents by exchanging the primitive polar bilayer with lipophilic, disulfide dendritic ligands is reported. The presence of such a thick nonpolar organic shell around these large nanoparticles enhances their stabilization against aggregation, in addition to enabling their transfer into a variety of solvents such as chloroform, toluene or tetrahydrofuran. Upon the slow evaporation of a chloroform suspension deposited on a solid support, the dendronized hybrids were found to self-assemble into ring structures of various diameters. Moreover, their self-assembly at the liquid-air interface affords the formation of fairly long-range ordered monolayers, over large areas, that can then be entirely transferred onto solid substrates. Electronic supplementary information (ESI) available: TEM microscope images. See DOI: 10.1039/c6nr03404g

The role of ultra-fast solvent evaporation on the directed self-assembly of block polymer thin films

NASA Astrophysics Data System (ADS)

Drapes, Chloe; Nelson, G.; Grant, M.; Wong, J.; Baruth, A.

The directed self-assembly of nano-structures in block polymer thin films viasolvent vapor annealing is complicated by several factors, including evaporation rate. Solvent vapor annealing exposes a disordered film to solvent(s) in the vapor phase, increasing mobility and tuning surface energy, with the intention of producing an ordered structure. Recent theoretical predictions reveal the solvent evaporation affects the resultant nano-structuring. In a competition between phase separation and kinetic trapping during drying, faster solvent removal can enhance the propagation of a given morphology into the bulk of the thin film down to the substrate. Recent construction of a purpose-built, computer controlled solvent vapor annealing chamber provides control over forced solvent evaporation down to 15 ms. This is accomplished using pneumatically actuated nitrogen flow into and out of the chamber. Furthermore, in situ spectral reflectance, with 10 ms temporal resolution, monitors the swelling and evaporation. Presently, cylinder-forming polystyrene-block-polylactide thin films were swollen with 40% (by volume) tetrahydrofuran, followed by immediate evaporation under a variety of designed conditions. This includes various evaporation times, ranging from 15 ms to several seconds, and four unique rate trajectories, including linear, exponential, and combinations. Atomic force microscopy reveals specific surface, free and substrate, morphologies of the resultant films, dependent on specific evaporation conditions. Funded by the Clare Boothe Luce Foundation and Nebraska EPSCoR.

Long-range single domain array of a 5 nm pattern of supramolecules via solvent annealing in a double-sandwich cell.

PubMed

Kwon, Kiok; Park, Kangho; Jung, Hee-Tae

2018-05-10

In nanotechnology and microelectronics research, the generation of an ultradense, single-grain nanostructure with a long-range lateral order is challenging. In this paper, we report upon a new solvent-annealing method using a double-sandwich confinement to promote the formation of a large-area, single-domain array (>0.3 × 0.3 mm2) of supramolecular cylinders with a small feature size (4.7 nm). The in situ GISAXS experiment result shows the ordering process during solvent evaporation. The diffusion of the solvent molecules led to the disassembly of the supramolecules confined between the top and bottom surfaces and their subsequent mobilization, thereby producing a highly ordered hexagonal array of supramolecular materials under the double-sandwich confinement upon solvent evaporation. In addition, two key factors were found to be crucial in this process for generating highly-ordered supramolecular building blocks: (i) the presence of a top coat during solvent evaporation to provide a geometric confinement template, and (ii) the control of the solvent evaporation rate during the solvent evaporation step to provide the dendrimer sufficient time to self-assemble into the highly ordered state over a large area. Our developed approach, which can be extended to be used for a large family of supramolecules, is of critical importance in providing a new bottom-up lithographic method based on supramolecular self-assembly.

Structure of block copolymer micelles in the presence of co-solvents

NASA Astrophysics Data System (ADS)

Robertson, Megan; Wang, Shu; Le, Kim Mai; Piemonte, Rachele; Madsen, Louis

2015-03-01

Amphiphilic block copolymer micelles in water are under broad exploration for drug delivery applications due to their high loading capacity and targeted drug delivery. We aim to understand the kinetic and thermodynamic processes that underlie the self-assembly of diblock copolymer micelle systems. The present work focuses on diblock copolymers containing poly(ethylene oxide) (a hydrophilic polymer) and polycaprolactone (a hydrophobic polymer), which spontaneously self-assemble into spherical micelles in water. Addition of a common good solvent (a co-solvent) for both of the constituting blocks, such as tetrahydrofuran (THF), reduces the interfacial tension at the core-corona interface. We are currently investigating the effect of this phenomenon on the micelle structural properties, using scattering experiments and nuclear magnetic resonance. We have characterized the hydrodynamic radius, core radius, corona thickness, aggregation number, degree of swelling of the micelle core with the co-solvent, and unimer (free chain) concentration, as a function of the co-solvent concentration. Fundamental knowledge from these studies will inform design of drug delivery systems by allowing us to tailor micelle properties for optimal cargo loading.

Self-assembly of short amyloidogenic peptides at the air-water interface.

PubMed

Chaudhary, Nitin; Nagaraj, Ramakrishnan

2011-08-01

Short peptide stretches in amyloidogenic proteins can form amyloid fibrils in vitro and have served as good models for studying amyloid fibril formation. Recently, these amyloidogenic peptides have gained considerable attention, as non-amyloid ordered structures can be obtained from these peptides by carefully tuning the conditions of self-assembly, especially pH, temperature and presence of organic solvents. We have examined the effect of surface pressure on the self-assembled structures of two amyloidogenic peptides, Pβ(2)m (Ac-DWSFYLLYYTEFT-am) and AcPHF6 (Ac-VQIVYK-am) at the air-water interface when deposited from different solvents. Both the peptides are surface-active and form Thioflavin T (ThT) positive structures at the air-water interface. There is considerable hysteresis in the compression and expansion isotherms, suggesting the occurrence of structural rearrangements during compression. Preformed Pβ(2)m fibrillar structures at the air-water interface are disrupted as peptide is compressed to lower molecular areas but restored if the film is expanded, suggesting that the process is reversible. AcPHF6, on the other hand, shows largely sheet-like structures at lower molecular areas. The solvents used for dissolution of the peptides appear to influence the nature of the aggregates formed. Our results show that like hydrostatic pressure, surface pressure can also be utilized for modulating the self-assembly of the amyloidogenic and self-assembling peptides. Copyright © 2011 Elsevier Inc. All rights reserved.

Fast assembly of ordered block copolymer nanostructures through microwave annealing.

PubMed

Zhang, Xiaojiang; Harris, Kenneth D; Wu, Nathanael L Y; Murphy, Jeffrey N; Buriak, Jillian M

2010-11-23

Block copolymer self-assembly is an innovative technology capable of patterning technologically relevant substrates with nanoscale precision for a range of applications from integrated circuit fabrication to tissue interfacing, for example. In this article, we demonstrate a microwave-based method of rapidly inducing order in block copolymer structures. The technique involves the usage of a commercial microwave reactor to anneal block copolymer films in the presence of appropriate solvents, and we explore the effect of various parameters over the polymer assembly speed and defect density. The approach is applied to the commonly used poly(styrene)-b-poly(methyl methacrylate) (PS-b-PMMA) and poly(styrene)-b-poly(2-vinylpyridine) (PS-b-P2VP) families of block copolymers, and it is found that the substrate resistivity, solvent environment, and anneal temperature all critically influence the self-assembly process. For selected systems, highly ordered patterns were achieved in less than 3 min. In addition, we establish the compatibility of the technique with directed assembly by graphoepitaxy.

Thermodynamics, morphology, and kinetics of early-stage self-assembly of π-conjugated oligopeptides

DOE Office of Scientific and Technical Information (OSTI.GOV)

None, None

Synthetic oligopeptides containing π-conjugated cores self-assemble novel materials with attractive electronic and photophysical properties. All-atom, explicit solvent molecular dynamics simulations of Asp-Phe-Ala-Gly-OPV3-Gly-Ala-Phe-Asp peptides were used to parameterize an implicit solvent model to simulate early-stage self-assembly. Under low-pH conditions, peptides assemble into β-sheet-like stacks with strongly favorable monomer association free energies of ΔF ≈ -25kBT. Aggregation at high-pH produces disordered aggregates destabilized by Coulombic repulsion between negatively charged Asp termini (ΔF ≈ -5kBT). In simulations of hundreds of monomers over 70 ns we observe the spontaneous formation of up to undecameric aggregates under low-pH conditions. Modeling assembly as a continuous-time Markovmore » process, we infer transition rates between different aggregate sizes and microsecond relaxation times for early-stage assembly. Our data suggests a hierarchical model of assembly in which peptides coalesce into small clusters over tens of nanoseconds followed by structural ripening and diffusion limited aggregation on longer time scales. This work provides new molecular-level understanding of early-stage assembly, and a means to study the impact of peptide sequence and aromatic core chemistry upon the thermodynamics, assembly kinetics, and morphology of the supramolecular aggregates.« less

Thermodynamics, morphology, and kinetics of early-stage self-assembly of π-conjugated oligopeptides

DOE PAGES

None, None

2016-03-22

Synthetic oligopeptides containing π-conjugated cores self-assemble novel materials with attractive electronic and photophysical properties. All-atom, explicit solvent molecular dynamics simulations of Asp-Phe-Ala-Gly-OPV3-Gly-Ala-Phe-Asp peptides were used to parameterize an implicit solvent model to simulate early-stage self-assembly. Under low-pH conditions, peptides assemble into β-sheet-like stacks with strongly favorable monomer association free energies of ΔF ≈ -25kBT. Aggregation at high-pH produces disordered aggregates destabilized by Coulombic repulsion between negatively charged Asp termini (ΔF ≈ -5kBT). In simulations of hundreds of monomers over 70 ns we observe the spontaneous formation of up to undecameric aggregates under low-pH conditions. Modeling assembly as a continuous-time Markovmore » process, we infer transition rates between different aggregate sizes and microsecond relaxation times for early-stage assembly. Our data suggests a hierarchical model of assembly in which peptides coalesce into small clusters over tens of nanoseconds followed by structural ripening and diffusion limited aggregation on longer time scales. This work provides new molecular-level understanding of early-stage assembly, and a means to study the impact of peptide sequence and aromatic core chemistry upon the thermodynamics, assembly kinetics, and morphology of the supramolecular aggregates.« less

Homopolymer Micelles in Heterogeneous Solvent Mixtures

PubMed Central

Basu, Subhadeep; Vutukuri, Dharma Rao

2008-01-01

Amphiphilic homopolymers containing a hydrophilic and a hydrophobic functionality in each monomer unit have been shown to form polar or apolar containers depending on the solvent environment. When presented with a mixture of solvents, these polymeric containers are capable of releasing certain guest molecules. The fundamental mechanism behind these properties is investigated and the utility of these assemblies in separations has been demonstrated with an example. PMID:16316219

Self-assembly mechanism of 1,3:2,4-di(3,4-dichlorobenzylidene)-D-sorbitol and control of the supramolecular chirality.

PubMed

Li, Jingjing; Fan, Kaiqi; Guan, Xidong; Yu, Yingzhe; Song, Jian

2014-11-11

Dibenzylidene-D-sorbitol (DBS) and its derivatives are known to form gels in organic solvents; however, the mechanism of the gel formation has been a subject of much debate. The present work is undertaken to elucidate the organization mechanism of a DBS derivative, 1,3:2,4-di(3,4-dichlorobenzylidene)-D-sorbitol (DCDBS), by taking into account the solvent effects and comparing the experiment data with theoretical calculation. These molecules form smooth nonhelical fibers with a rest circular dichroism (CD) signal in polar solvents, in contrast to rope-liked left-helical fibers with a strong negative CD signal observed in nonpolar solvents. The molecular complexes thus formed were characterized by means of Fourier transform infrared spectra, ultraviolet-visible spectra, X-ray diffraction patterns, static contact angles, and theoretical calculations. It was proposed that the interactions between the gelator and the solvents could subtly change the stacking of the molecules and hence their self-assembled nanostructures. In nonpolar solvents, the gelator molecules appear as a distorted T-shaped structure with the 6-OH forming intermolecular hydrogen bonds with the acetal oxygens of adjacent gelator molecule. In addition, because of differential stacking interactions on both sides of the 10-member ring skeleton of the gelator, the oligomers may assemble in a helix fashion to minimize the energy, leading to helical fibers. In polar solvents, however, the gelator molecules show a rigid planelike structure and thus stack on top of each other because of strong parallel-displaced π interactions. The balanced driving force on both sides of the 10-member ring skeleton made it difficult for the dimers to bend, thus resulting in nonhelical nanostructure. As expected from the mechanisms proposed here, twisted ribbon fibers with a medium strength CD signal were obtained when solvents of different polarities were mixed. Thus, solvent effects revealed in this work represent an effective means of realizing in situ tuning of nanostructures and control of the expression of chirality at supramolecular levels.

Time-resolved viscoelastic properties of self-assembling iron oxide nanocube superlattices probed by quartz crystal microbalance with dissipation monitoring.

PubMed

Kapuscinski, Martin; Agthe, Michael; Bergström, Lennart

2018-07-15

Self-assembly of nanoparticles into superlattices can be used to create hierarchically structured materials with tailored functions. We have used the surface sensitive quartz crystal microbalance with dissipation monitoring (QCM-D) technique in combination with video microscopy (VM) to obtain time-resolved information on the mass increase and rheological properties of evaporation-induced self-assembly of nanocubes. We have recorded the frequency and dissipation shifts during growth and densification of superlattices formed by self-assembly of oleic acid capped, truncated iron oxide nanocubes and analyzed the time-resolved QCM-D data using a Kelvin-Voigt viscoelastic model. We show that the nanoparticles first assemble into solvent-containing arrays dominated by a viscous response followed by a solvent-releasing step that results in the formation of rigid and well-ordered superlattices. Our findings demonstrate that QCM-D can be successfully used to follow self-assembly and assist in the design of optimized routes to produce well-ordered superlattices. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

Cooperation of Amphiphilicity and Crystallization for Regulating the Self-Assembly of Poly(ethylene glycol)-block-poly(lactic acid) Copolymers.

PubMed

Wang, Zhen; Cao, Yuanyuan; Song, Jiaqi; Xie, Zhigang; Wang, Yapei

2016-09-20

Tuning the amphiphilicity of block copolymers has been extensively exploited to manipulate the morphological transition of aggregates. The introduction of crystallizable moieties into the amphiphilic copolymers also offers increasing possibilities for regulating self-assembled structures. In this work, we demonstrate a detailed investigation of the self-assembly behavior of amphiphilic poly(ethylene glycol)-block-poly(l-lactic acid) (PEG-b-PLLA) diblock copolymers with the assistance of a common solvent in aqueous solution. With a given length of the PEG block, the molecular weight of the PLA block has great effect on the morphologies of self-assembled nanoaggregates as a result of varying molecular amphiphilicity and polymer crystallization. Common solvents including N,N-dimethylformamide, dioxane, and tetrahydrofuran involved in the early stage of self-assembly led to the change in chain configuration, which further influences the self-assembly of block copolymers. This study expanded the scope of PLA-based copolymers and proposed a possible mechanism of the sphere-to-lozenge and platelet-to-cylinder morphological transitions.

Centrifugal contactor modified for end stage operation in a multistage system

DOEpatents

Jubin, Robert T.

1990-01-01

A cascade formed of a plurality of centrifugal contactors useful for countercurrent solvent extraction processes such as utilizable for the reprocessing of nuclear reactor fuels is modified to permit operation in the event one or both end stages of the cascade become inoperative. Weir assemblies are connected to each of the two end stages by suitable conduits for separating liquids discharged from an inoperative end stage based upon the weight of the liquid phases uses in the solvent extraction process. The weir assembly at one end stage is constructed to separate and discharge the heaviest liquid phase while the weir assembly at the other end stage is constructed to separate and discharge the lightest liquid phase. These weir assemblies function to keep the liquid discharge from an inoperative end stages on the same weight phase a would occur from an operating end stage.

Controlled Self-Assembly of Low-Dimensional Alq3 Nanostructures from 1D Nanowires to 2D Plates via Intermolecular Interactions

NASA Astrophysics Data System (ADS)

Gu, Jianmin; Yin, Baipeng; Fu, Shaoyan; Jin, Cuihong; Liu, Xin; Bian, Zhenpan; Li, Jianjun; Wang, Lu; Li, Xiaoyu

2018-03-01

Due to the intense influence of the shape and size of the photon building blocks on the limitation and guidance of optical waves, an important strategy is the fabrication of different structures. Herein, organic semiconductor tris-(8-hydroxyquinoline)aluminium (Alq3) nanostructures with controllable morphology, ranging from one-dimensional nanowires to two-dimensional plates, have been prepared through altering intermolecular interactions with employing the anti-solvent diffusion cooperate with solvent-volatilization induced self-assembly method. The morphologies of the formed nanostructures, which are closely related to the stacking modes of the molecules, can be exactly controlled by altering the polarity of anti-solvents that can influence various intermolecular interactions. The synthesis strategy reported here can potentially be extended to other functional organic nanomaterials.

Fabrication of microspheres via solvent volatization induced aggregation of self-assembled nanomicellar structures and their use as a pH-dependent drug release system.

PubMed

Zhang, Lidong; Jeong, Young-Il; Zheng, Sudan; Suh, Hongsuk; Kang, Dae Hwan; Kim, Il

2013-01-08

A series of oleamide derivatives, (C(18)H(34)NO)(2)(CH(2))(n) [n = 2 (1a), 3 (1b), 4 (1c), or 6 (1d); C(18)H(34)NO = oleic amide fragment] and (C(18)H(34)NO)(CH(2))(6)NH(2) (2), have been synthesized and their self-assembly is investigated in ethanol/water media. Self-assembly of 1a and 1b in ethanol/water (1/0.1 v/v) solution (5 mg mL(-1)) yields microspheres (MSs) with the average diameter ∼10 μm via a gradual temperature reduction and solvent volatilization process. Under the same self-assembly conditions, microrods (average diameter ∼6 μm and several tens of micrometers in length), micronecklace-like, and shape-irregular microparticles are formed from the self-assembly of 1c, 1d, and 2, respectively. The kinetics of evolution for their self-assemblies by dynamic light scattering technique and in situ observation by optical microscopy reveals that the microstructures formation is from a well-behaved aggregation of nanoscale micelles induced by solvent volatilization. The FT-IR and temperature-dependent (1)H-NMR spectra demonstrate the hydrogen bonding force and π-π stacking, which drove the self-assembly of all oleamide derivatives in ethanol/water. Among the fabricated microstructures, the MSs from 1a exhibit the best dispersity, which thus have been used as a scaffold for the in vitro release of doxorubicin. The results demonstrate a pH-sensitive release process, enhanced release specifically at low pH 5.2.

Universal calculational recipe for solvent-mediated potential: based on a combination of integral equation theory and density functional theory

NASA Astrophysics Data System (ADS)

Zhou, Shiqi

2004-07-01

A universal formalism, which enables calculation of solvent-mediated potential (SMP) between two equal or non-equal solute particles with any shape immersed in solvent reservior consisting of atomic particle and/or polymer chain or their mixture, is proposed by importing a density functional theory externally into OZ equation systems. Only if size asymmetry of the solvent bath components is moderate, the present formalism can calculate the SMP in any complex fluids at the present development stage of statistical mechanics, and therefore avoids all of limitations of previous approaches for SMP. Preliminary calculation indicates the reliability of the present formalism.

Directed Self-Assembly of Triblock Copolymer on Chemical Patterns for Sub-10-nm Nanofabrication via Solvent Annealing.

PubMed

Xiong, Shisheng; Wan, Lei; Ishida, Yoshihito; Chapuis, Yves-Andre; Craig, Gordon S W; Ruiz, Ricardo; Nealey, Paul F

2016-08-23

Directed self-assembly (DSA) of block copolymers (BCPs) is a leading strategy to pattern at sublithographic resolution in the technology roadmap for semiconductors and is the only known solution to fabricate nanoimprint templates for the production of bit pattern media. While great progress has been made to implement block copolymer lithography with features in the range of 10-20 nm, patterning solutions below 10 nm are still not mature. Many BCP systems self-assemble at this length scale, but challenges remain in simultaneously tuning the interfacial energy atop the film to control the orientation of BCP domains, designing materials, templates, and processes for ultra-high-density DSA, and establishing a robust pattern transfer strategy. Among the various solutions to achieve domains that are perpendicular to the substrate, solvent annealing is advantageous because it is a versatile method that can be applied to a diversity of materials. Here we report a DSA process based on chemical contrast templates and solvent annealing to fabricate 8 nm features on a 16 nm pitch. To make this possible, a number of innovations were brought in concert with a common platform: (1) assembling the BCP in the phase-separated, solvated state, (2) identifying a larger process window for solvated triblock vs diblock BCPs as a function of solvent volume fraction, (3) employing templates for sub-10-nm BCP systems accessible by lithography, and (4) integrating a robust pattern transfer strategy by vapor infiltration of organometallic precursors for selective metal oxide synthesis to prepare an inorganic hard mask.

Hydrogen Bonding Stabilized Self-Assembly of Inorganic Nanoparticles: Mechanism and Collective Properties.

PubMed

Yue, Mingli; Li, Yanchun; Hou, Ying; Cao, Wenxin; Zhu, Jiaqi; Han, Jiecai; Lu, Zhongyuan; Yang, Ming

2015-06-23

Developing a simple and efficient method to organize nanoscale building blocks into ordered superstructures, understanding the mechanism for self-assembly and revealing the essential collective properties are crucial steps toward the practical use of nanostructures in nanotechnology-based applications. In this study, we showed that the high-yield formation of ZnO nanoparticle chains with micrometer length can be readily achieved by the variation of solvents from methanol to water. Spectroscopic studies confirmed the solvent effect on the surface properties of ZnO nanoparticles, which were found to be critical for the formation of anisotropic assemblies. Quantum mechanical calculations and all atom molecular dynamic simulations indicated the contribution of hydrogen bonding for stabilizing the structure in water. Dissipative particle dynamics further revealed the importance of solvent-nanoparticle interactions for promoting one-dimensional self-assembly. The branching of chains was found upon aging, resulting in the size increase of the ensembles and network formation. Steady-state and time-resolved luminescent spectroscopes, which probed the variation of defect-related emission, revealed stronger Forster resonance energy transfer (FRET) between nanoparticles when the chain networks were formed. The high efficiency of FRET quenching can be ascribed to the presence of multiple energy transfer channels, as well as the short internanoparticle distances and the dipole alignment.

Proton triggered circularly polarized luminescence in orthogonal- and co-assemblies of chiral gelators with achiral perylene bisimide.

PubMed

Han, Dongxue; Han, Jianlei; Huo, Shengwei; Qu, Zuoming; Jiao, Tifeng; Liu, Minghua; Duan, Pengfei

2018-05-29

The orthogonal- or co-assembly of achiral perylene bisimide (PBI) with chiral gelators can be regulated by solvents. While the coassembly leads to the formation of chiroptical nanofibers through chirality transfer, the orthogonal assemblies could not. Moreover, protonation on the coassembled nanofibers could light up the circularly polarized luminescence (CPL).

Thermodynamic and kinetic control of charged, amphiphilic triblock copolymer assembly via interaction with organic counterions in solvent mixtures

NASA Astrophysics Data System (ADS)

Cui, Honggang

2007-12-01

Amphiphilic block copolymers, consisting of at least two types of monomers with different affinity to the dissolving solvent(s), have been recognized as a molecular building unit for their chemical tunability and design flexibility. Amphiphilic block copolymers with a chargeable block have structural features of polyelectrolytes, block copolymers and surfactants. The combination of these different features offers great flexibility for developing novel assembled morphologies at the nanoscale and outstanding ability to control and manipulate those morphologies. The nanostructures, formed from the spontaneous association of amphiphilic block copolymer in selective solvents, show promise for applications in nanotechnology and pharmaceuticals, including drug delivery, tissue engineering and bio-imaging. A basic knowledge of their modes of self-assembly and their correspondence to application-related properties is just now being developed and poses a considerable scientific challenge. The goal of this dissertation is to investigate the associative behavior of charged, amphiphilic block copolymers in solvent mixtures while in the presence of organic counterions. Self-assembly of poly (acrylic acid)- block-poly (methyl acrylate)-block-polystyrene (PAA- b-PMA-b-PS) triblock copolymers produces nanodomains in THF/water solution specifically through the interaction with organic counterions (polyamines). These assembled structures can include classic micelles (spheres, cylinders and vesicles), but, more importantly, include non-classic micelles (disks, toroids, branched micelles and segmented micelles). Each micelle structure is stable and reproducible at different assembly conditions. The assembled micellar structures depend on not only solution components (thermodynamics) but also mixing procedure and consequent self-assembly pathway (kinetics). The key factors that determine the thermodynamic interactions that partially define the assembled structures and the kinetic assembly process include THF/water ratio, PS block length, the type and amount of organic counterions, and the mixing pathway. Their formation mechanism has been investigated from three aspects: (i) the chain structure of organic counterions, including spacer length, chain hydrophobicity between ionizable groups and the number of ionizable groups (amine group); (ii) molecular structure of the triblock copolymer, including block length of polystyrene and chain architecture; (iii) relative variation of the components, such as different ratios of THF to water and the different ratios of amine groups to acid groups. The first example of a novel micelle formed was the toroidal micelle. The toroidal micelle morphology, which is theoretically predicted but rarely observed, has been produced by the self assembly of PAA99- b-PMA73-b-PS66 in combination with 2,2-(ethylenedioxy)diethylamine (EDDA) and mixed THF/H2O solvent. It was found that toroids can be constructed by two mechanisms: elimination of energetically unfavored cylindrical micelle endcaps or perforation of disk-like micelles. Three-fold junctions were formed as intermediate structures to facilitate toroidal formation from cylindrical micelles. In order to construct toroids from cylindrical micelles, three requirements must be met: lower bending modulus (flexibility of cylinders), selfattraction between cylinders, and extra endcapping energy originating from chain packing frustration. Extremely high energy spheres can also fuse into toroids. Disk-like micelles can transform into a toroidal morphology when cylindrical packing geometry was initiated along the rims of disk-like micelles via solvent mixing that eventually perforated the disk center. The toroidal morphology can be kinetically trapped by either ridding the system of organic solvent or chemically crosslinking the PAA corona with EDDA via addition of 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide methiodide (DPEM). The interaction of positively-charged, multivalent organic amines with the negatively-charged PAA corona plays a decisive role in the formation of these micelles. Inter-chain binding from the interaction of the two amine end groups of diamines with acid groups from different PAA corona blocks governs the final assembled structures. Diamines with hydrophilic spacers induced the formation of micelles with larger interfacial curvature as the spacer length increased. Disk-like micelles, cylindrical micelles or spherical micelles were observed with the gradual increase of hydrophilic spacer length. Diamines with variable hydrophobic spacers showed a similar effect when the spacer length was less than six methylene units. Application of longer hydrophobic diamines had a reverse effect on the interfacial curvature. This effect was attributed to the interaction of hydrophobic diamine hydrocarbon linking chains with the PMA-b-PS hydrophobic core. These findings indicate an easy method to tune micelle structure with multivalent organic counterions. (Abstract shortened by UMI.)

Ultrahigh Molecular Weight Linear Block Copolymers: Rapid Access by Reversible-Deactivation Radical Polymerization and Self- Assembly into Large Domain Nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mapas, Jose Kenneth D.; Thomay, Tim; Cartwright, Alexander N.

2016-05-05

Block copolymer (BCP) derived periodic nanostructures with domain sizes larger than 150 nm present a versatile platform for the fabrication of photonic materials. So far, the access to such materials has been limited to highly synthetically involved protocols. Herein, we report a simple, “user-friendly” method for the preparation of ultrahigh molecular weight linear poly(solketal methacrylate-b-styrene) block copolymers by a combination of Cu-wire-mediated ATRP and RAFT polymerizations. The synthesized copolymers with molecular weights up to 1.6 million g/mol and moderate dispersities readily assemble into highly ordered cylindrical or lamella microstructures with domain sizes as large as 292 nm, as determined bymore » ultra-small-angle x-ray scattering and scanning electron microscopy analyses. Solvent cast films of the synthesized block copolymers exhibit stop bands in the visible spectrum correlated to their domain spacings. The described method opens new avenues for facilitated fabrication and the advancement of fundamental understanding of BCP-derived photonic nanomaterials for a variety of applications.« less

Speeding up the self-assembly of a DNA nanodevice using a variety of polar solvents

NASA Astrophysics Data System (ADS)

Kang, Di; Duan, Ruixue; Tan, Yerpeng; Hong, Fan; Wang, Boya; Chen, Zhifei; Xu, Shaofang; Lou, Xiaoding; Wei, Wei; Yurke, Bernard; Xia, Fan

2014-11-01

The specific recognition and programmable assembly properties make DNA a potential material for nanodevices. However, the more intelligent the nanodevice is, the more complicated the structure of the nanodevice is, which limits the speed of DNA assembly. Herein, to address this problem, we investigate the performance of DNA Strand Displacement Reaction (DSDR) in a mixture of polar organic solvents and aqueous buffer and demonstrate that the organic polar solvent can speed up DNA self-assembly efficiently. Taking DSDR in 20% ethanol as an example, first we have demonstrated that the DSDR is highly accelerated in the beginning of the reaction and it can complete 60% of replacement reactions (160% enhancement compared with aqueous buffer) in the first 300 seconds. Secondly, we calculated that the ΔΔG of the DSDR in 20% ethanol (-18.2 kcal mol-1) is lower than that in pure aqueous buffer (-32.6 kcal mol-1), while the activation energy is lowered by introducing ethanol. Finally, we proved that the DSDR on the electrode surface can also be accelerated using this simple strategy. More importantly, to test the efficacy of this approach in nanodevices with a complicated and slow DNA self-assembly process, we apply this strategy in the hybridization chain reaction (HCR) and prove the acceleration is fairly obvious in 20% ethanol, which demonstrates the feasibility of the proposed strategy in DNA nanotechnology and DNA-based biosensors.The specific recognition and programmable assembly properties make DNA a potential material for nanodevices. However, the more intelligent the nanodevice is, the more complicated the structure of the nanodevice is, which limits the speed of DNA assembly. Herein, to address this problem, we investigate the performance of DNA Strand Displacement Reaction (DSDR) in a mixture of polar organic solvents and aqueous buffer and demonstrate that the organic polar solvent can speed up DNA self-assembly efficiently. Taking DSDR in 20% ethanol as an example, first we have demonstrated that the DSDR is highly accelerated in the beginning of the reaction and it can complete 60% of replacement reactions (160% enhancement compared with aqueous buffer) in the first 300 seconds. Secondly, we calculated that the ΔΔG of the DSDR in 20% ethanol (-18.2 kcal mol-1) is lower than that in pure aqueous buffer (-32.6 kcal mol-1), while the activation energy is lowered by introducing ethanol. Finally, we proved that the DSDR on the electrode surface can also be accelerated using this simple strategy. More importantly, to test the efficacy of this approach in nanodevices with a complicated and slow DNA self-assembly process, we apply this strategy in the hybridization chain reaction (HCR) and prove the acceleration is fairly obvious in 20% ethanol, which demonstrates the feasibility of the proposed strategy in DNA nanotechnology and DNA-based biosensors. Electronic supplementary information (ESI) available: Experimental procedures and analytical data are provided. See DOI: 10.1039/c4nr02257b

Speeding up the self-assembly of a DNA nanodevice using a variety of polar solvents.

PubMed

kang, Di; Duan, Ruixue; Tan, Yerpeng; Hong, Fan; Wang, Boya; Chen, Zhifei; Xu, Shaofang; Lou, Xiaoding; Wei, Wei; Yurke, Bernard; Xia, Fan

2014-11-06

The specific recognition and programmable assembly properties make DNA a potential material for nanodevices. However, the more intelligent the nanodevice is, the more complicated the structure of the nanodevice is, which limits the speed of DNA assembly. Herein, to address this problem, we investigate the performance of DNA Strand Displacement Reaction (DSDR) in a mixture of polar organic solvents and aqueous buffer and demonstrate that the organic polar solvent can speed up DNA self-assembly efficiently. Taking DSDR in 20% ethanol as an example, first we have demonstrated that the DSDR is highly accelerated in the beginning of the reaction and it can complete 60% of replacement reactions (160% enhancement compared with aqueous buffer) in the first 300 seconds. Secondly, we calculated that the ΔΔG of the DSDR in 20% ethanol (-18.2 kcal mol(-1)) is lower than that in pure aqueous buffer (-32.6 kcal mol(-1)), while the activation energy is lowered by introducing ethanol. Finally, we proved that the DSDR on the electrode surface can also be accelerated using this simple strategy. More importantly, to test the efficacy of this approach in nanodevices with a complicated and slow DNA self-assembly process, we apply this strategy in the hybridization chain reaction (HCR) and prove the acceleration is fairly obvious in 20% ethanol, which demonstrates the feasibility of the proposed strategy in DNA nanotechnology and DNA-based biosensors.

Self-assembly of water-soluble nanocrystals

DOEpatents

Fan, Hongyou [Albuquerque, NM; Brinker, C Jeffrey [Albuquerque, NM; Lopez, Gabriel P [Albuquerque, NM

2012-01-10

A method for forming an ordered array of nanocrystals where a hydrophobic precursor solution with a hydrophobic core material in an organic solvent is added to a solution of a surfactant in water, followed by removal of a least a portion of the organic solvent to form a micellar solution of nanocrystals. A precursor co-assembling material, generally water-soluble, that can co-assemble with individual micelles formed in the micellar solution of nanocrystals can be added to this micellar solution under specified reaction conditions (for example, pH conditions) to form an ordered-array mesophase material. For example, basic conditions are used to precipitate an ordered nanocrystal/silica array material in bulk form and acidic conditions are used to form an ordered nanocrystal/silica array material as a thin film.

Molecular architecture of the human Mediator-RNA polymerase II-TFIIF assembly.

PubMed

Bernecky, Carrie; Grob, Patricia; Ebmeier, Christopher C; Nogales, Eva; Taatjes, Dylan J

2011-03-01

The macromolecular assembly required to initiate transcription of protein-coding genes, known as the Pre-Initiation Complex (PIC), consists of multiple protein complexes and is approximately 3.5 MDa in size. At the heart of this assembly is the Mediator complex, which helps regulate PIC activity and interacts with the RNA polymerase II (pol II) enzyme. The structure of the human Mediator-pol II interface is not well-characterized, whereas attempts to structurally define the Mediator-pol II interaction in yeast have relied on incomplete assemblies of Mediator and/or pol II and have yielded inconsistent interpretations. We have assembled the complete, 1.9 MDa human Mediator-pol II-TFIIF complex from purified components and have characterized its structural organization using cryo-electron microscopy and single-particle reconstruction techniques. The orientation of pol II within this assembly was determined by crystal structure docking and further validated with projection matching experiments, allowing the structural organization of the entire human PIC to be envisioned. Significantly, pol II orientation within the Mediator-pol II-TFIIF assembly can be reconciled with past studies that determined the location of other PIC components relative to pol II itself. Pol II surfaces required for interacting with TFIIB, TFIIE, and promoter DNA (i.e., the pol II cleft) are exposed within the Mediator-pol II-TFIIF structure; RNA exit is unhindered along the RPB4/7 subunits; upstream and downstream DNA is accessible for binding additional factors; and no major structural re-organization is necessary to accommodate the large, multi-subunit TFIIH or TFIID complexes. The data also reveal how pol II binding excludes Mediator-CDK8 subcomplex interactions and provide a structural basis for Mediator-dependent control of PIC assembly and function. Finally, parallel structural analysis of Mediator-pol II complexes lacking TFIIF reveal that TFIIF plays a key role in stabilizing pol II orientation within the assembly.

Amphiphilic Polysaccharide Block Copolymers for pH-Responsive Micellar Nanoparticles.

PubMed

Breitenbach, Benjamin B; Schmid, Ira; Wich, Peter R

2017-09-11

A full polysaccharide amphiphilic block copolymer was prepared from end group-functionalized dextrans using copper-mediated azide-alkyne click chemistry. Sufficient modification of the reducing end in both blocks was achieved by microwave-enhanced reductive amination in a borate-buffer/methanol solvent system. The combination of a hydrophilic dextran block with a hydrophobic acetalated dextran block results in an amphiphilic structure that turns water-soluble upon acid treatment. The material has a low critical micelle concentration and self-assembles in water to spherical micellar nanoparticles. The formed nanoparticles have a narrow size distribution below 70 nm in diameter and disassemble in slightly acidic conditions. The amphiphilic polysaccharide system shows low toxicity and can stabilize the hydrophobic model drug curcumin in aqueous solutions over extended time periods.

Self-assembly of a chiral lipid gelator controlled by solvent and speed of gelation.

PubMed

Xue, Pengchong; Lu, Ran; Yang, Xinchun; Zhao, Li; Xu, Defang; Liu, Yan; Zhang, Hanzhuang; Nomoto, Hiroyuki; Takafuji, Makoto; Ihara, Hirotaka

2009-09-28

Glutamine derivative 1 with two-photon absorbing units has been synthesized and was found to show gelation ability in some solvents. Its self-assembly in the gel phase could be controlled by the solvent and speed of gelation. For example, in DMSO the organogelator self-assembled into H-aggregates with weak exciton coupling between the aromatic moieties. On the other hand, in DMSO/diphenyl ether (1:9, v/v) the molecules formed 1D aggregates, but with strong exciton coupling due to the small distance between the chromophores. Moreover, the formation of these two kinds of aggregates could be adjusted by the ratio of DMSO to diphenyl ether. In DMSO/toluene, DMSO/butanol, DMSO/butyl acetate, and DMSO/acetic acid systems similar results were observed. Therefore, conversion of the packing model occurs irrespective of the nature of the solvent. Notably, a unique sign inversion in the CD spectra could be realized by controlling the speed of gelation in the DMSO/diphenyl ether (1:9, v/v) system. It was found that a low speed of gelation induces the gelator to adopt a packing model with strong pi-pi interactions between the aromatic units. Moreover, the gels, when excited at 800 nm, emit strong green fluorescence and the quantum chemical calculations suggest that intramolecular charge transfer leads to two-photon absorption of the gelator molecule.

Mechanistic principles of colloidal crystal growth by evaporation-induced convective steering.

PubMed

Brewer, Damien D; Allen, Joshua; Miller, Michael R; de Santos, Juan M; Kumar, Satish; Norris, David J; Tsapatsis, Michael; Scriven, L E

2008-12-02

We simulate evaporation-driven self-assembly of colloidal crystals using an equivalent network model. Relationships between a regular hexagonally close-packed array of hard, monodisperse spheres, the associated pore space, and selectivity mechanisms for face-centered cubic microstructure propagation are described. By accounting for contact line rearrangement and evaporation at a series of exposed menisci, the equivalent network model describes creeping flow of solvent into and through a rigid colloidal crystal. Observations concerning colloidal crystal growth are interpreted in terms of the convective steering hypothesis, which posits that solvent flow into and through the pore space of the crystal may play a major role in colloidal self-assembly. Aspects of the convective steering and deposition of high-Peclet-number rigid spherical particles at a crystal boundary are inferred from spatially resolved solvent flow into the crystal. Gradients in local flow through boundary channels were predicted due to the channels' spatial distribution relative to a pinned free surface contact line. On the basis of a uniform solvent and particle flux as the criterion for stability of a particular growth plane, these network simulations suggest the stability of a declining {311} crystal interface, a symmetry plane which exclusively propagates fcc microstructure. Network simulations of alternate crystal planes suggest preferential growth front evolution to the declining {311} interface, in consistent agreement with the proposed stability mechanism for preferential fcc microstructure propagation in convective assembly.

A template-free solvent-mediated synthesis of high surface area boron nitride nanosheets for aerobic oxidative desulfurization.

PubMed

Wu, Peiwen; Zhu, Wenshuai; Chao, Yanhong; Zhang, Jinshui; Zhang, Pengfei; Zhu, Huiyuan; Li, Changfeng; Chen, Zhigang; Li, Huaming; Dai, Sheng

2016-01-04

Hexagonal boron nitride nanosheets (h-BNNs) with rather high specific surface area (SSA) are important two-dimensional layer-structured materials. Here, a solvent-mediated synthesis of h-BNNs revealed a template-free lattice plane control strategy that induced high SSA nanoporous structured h-BNNs with outstanding aerobic oxidative desulfurization performance.

Creating Quasi Two-Dimensional Cluster-Assembled Materials through Self-Assembly of a Janus Polyoxometalate-Silsesquioxane Co-Cluster.

PubMed

Wu, Han; Zhang, Yu-Qi; Hu, Min-Biao; Ren, Li-Jun; Lin, Yue; Wang, Wei

2017-05-30

Clusters are an important class of nanoscale molecules or superatoms that exhibit an amazing diversity in structure, chemical composition, shape, and functionality. Assembling two types of clusters is creating emerging cluster-assembled materials (CAMs). In this paper, we report an effective approach to produce quasi two-dimensional (2D) CAMs of two types of spherelike clusters, polyhedral oligomeric silsesquioxanes (POSS), and polyoxometalates (POM). To avoid macrophase separation between the two clusters, they are covalently linked to form a POM-POSS cocluster with Janus characteristics and a dumbbell shape. This Janus characteristics enables the cocluster to self-assemble into diverse nanoaggregates, as conventional amphiphilic molecules and macromolecules do, in selective solvents. In our study, we obtained micelles, vesicles, nanosheets, and nanoribbons by tuning the n-hexane content in mixed solvents of acetone and n-hexane. Ordered packing of clusters in the nanosheets and nanoribbons were directly visualized using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) technique. We infer that the increase of packing order results in the vesicle-to-sheet transition and the change in packing mode causes the sheet-to-ribbon transitions. Our findings have verified the effectivity of creating quasi 2D cluster-assembled materials though the cocluster self-assembly as a new approach to produce novel CAMs.

Interactions between Biological and Abiotic Pathways in the Reduction of Chlorinated Solvents

EPA Science Inventory

While biologically mediated reductive dechlorination continues to be a significant focus of chlorinated solvent remediation, there has been an increased interest in abiotic reductive processes for the remediation of chlorinated solvents. In situ chemical reduction (ISCR) uses zer...

Membranes with well-defined ions transport channels fabricated via solvent-responsive layer-by-layer assembly method for vanadium flow battery.

PubMed

Xu, Wanxing; Li, Xianfeng; Cao, Jingyu; Zhang, Hongzhang; Zhang, Huamin

2014-02-06

In this work we presented a general strategy for the fabrication of membranes with well-defined ions transport channels through solvent-responsive layer-by-layer assembly (SR-LBL). Multilayered poly (diallyldimethylammonium chloride) (PDDA) and poly (acrylic acid) (PAA) complexes were first introduced on the inner pore wall and the surface of sulfonated poly (ether ether ketone)/poly (ether sulfone) (PES/SPEEK) nanofiltration membranes to form ions transport channels with tuned radius. This type of membranes are highly efficient for the separators of batteries especially vanadium flow batteries (VFBs): the VFBs assembled with prepared membranes exhibit an outstanding performance in a wide current density range, which is much higher than that assembled with commercial Nafion 115 membranes. This idea could inspire the development of membranes for other flow battery systems, as well as create further progress in similar areas such as fuel cells, electro-dialysis, chlor-alkali cells, water electrolysis and so on.

Membranes with well-defined ions transport channels fabricated via solvent-responsive layer-by-layer assembly method for vanadium flow battery

PubMed Central

Xu, Wanxing; Li, Xianfeng; Cao, Jingyu; Zhang, Hongzhang; Zhang, Huamin

2014-01-01

In this work we presented a general strategy for the fabrication of membranes with well-defined ions transport channels through solvent-responsive layer-by-layer assembly (SR-LBL). Multilayered poly (diallyldimethylammonium chloride) (PDDA) and poly (acrylic acid) (PAA) complexes were first introduced on the inner pore wall and the surface of sulfonated poly (ether ether ketone)/poly (ether sulfone) (PES/SPEEK) nanofiltration membranes to form ions transport channels with tuned radius. This type of membranes are highly efficient for the separators of batteries especially vanadium flow batteries (VFBs): the VFBs assembled with prepared membranes exhibit an outstanding performance in a wide current density range, which is much higher than that assembled with commercial Nafion 115 membranes. This idea could inspire the development of membranes for other flow battery systems, as well as create further progress in similar areas such as fuel cells, electro-dialysis, chlor-alkali cells, water electrolysis and so on. PMID:24500376

Stimuli-controlled self-assembly of diverse tubular aggregates from one single small monomer

NASA Astrophysics Data System (ADS)

Shi, Qixun; Javorskis, Tomas; Bergquist, Karl-Erik; Ulčinas, Artūras; Niaura, Gediminas; Matulaitienė, Ieva; Orentas, Edvinas; Wärnmark, Kenneth

2017-04-01

The design and synthesis of new stimuli-responsive hydrogen-bonding monomers that display a diversity of self-assembly pathways is of central importance in supramolecular chemistry. Here we describe the aggregation properties of a simple, intrinsically C2-symmetric enantiopure bicyclic cavity compound bearing a terminally unsubstituted ureidopyrimidinone fragment fused with a pyrrole moiety in different solvents and in the absence and presence of C60 and C70 guests. The tetrameric cyclic aggregate is selectively obtained in chlorinated solvents, where only part of the available hydrogen bonding sites are utilized, whereas in toluene or upon addition of C70 guests, further aggregation into tubular supramolecular polymers is achieved. The open-end cyclic assemblies rearrange into a closed-shell capsule upon introduction of C60 with an accompanied symmetry breaking of the monomer. Our study demonstrates that a C60 switch can be used to simultaneously control the topology and occupancy of tubular assemblies resulting from the aggregation of small monomers.

Partitioning of residual D-limonene cleaner vapor among organic materials in weapons

DOE Office of Scientific and Technical Information (OSTI.GOV)

LeMay, J.D.

1993-03-01

D-limonene is a replacement solvent selected by Sandia and Allied-Signal to clean solder flux from electronics assemblies in firesets and programmers. D-limonene is much slower drying than the solvents it has replaced and this has raised concerns that residual quantities of the cleaner could be trapped in the electronics assemblies and eventually carried into warhead assemblies. This paper describes a study designed to evaluate how vapors from residual d-limonene cleaner would be partitioned among typical organic materials in a Livermore device. The goal was to identify possible compatibility problems arising from the use of d-limonene and, in particular, any interactionsmore » it may have with energetic materials. To predict the partitioning behavior of d-limonene, a simple model was developed and its predictions are compared to the experimental findings.« less

Self-assembly of organogels via new luminol imide derivatives: diverse nanostructures and substituent chain effect

PubMed Central

2013-01-01

Luminol is considered as an efficient sycpstem in electrochemiluminescence (ECL) measurements for the detection of hydrogen peroxide. In this paper, new luminol imide derivatives with different alkyl substituent chains were designed and synthesized. Their gelation behaviors in 26 solvents were tested as novel low molecular mass organic gelators. It was shown that the length and number of alkyl substituent chains linked to a benzene ring in gelators played a crucial role in the gelation behavior of all compounds in various organic solvents. Longer alkyl chains in molecular skeletons in present gelators are favorable for the gelation of organic solvents. Scanning electron microscope and atomic force microscope observations revealed that the gelator molecules self-assemble into different micro/nanoscale aggregates from a dot, flower, belt, rod, and lamella to wrinkle with change of solvents. Spectral studies indicated that there existed different H-bond formations and hydrophobic forces, depending on the alkyl substituent chains in molecular skeletons. The present work may give some insight to the design and characteristic of new versatile soft materials and potential ECL biosensors with special molecular structures. PMID:23758979

Self-assembly of organogels via new luminol imide derivatives: diverse nanostructures and substituent chain effect

NASA Astrophysics Data System (ADS)

Jiao, Tifeng; Huang, Qinqin; Zhang, Qingrui; Xiao, Debao; Zhou, Jingxin; Gao, Faming

2013-06-01

Luminol is considered as an efficient sycpstem in electrochemiluminescence (ECL) measurements for the detection of hydrogen peroxide. In this paper, new luminol imide derivatives with different alkyl substituent chains were designed and synthesized. Their gelation behaviors in 26 solvents were tested as novel low molecular mass organic gelators. It was shown that the length and number of alkyl substituent chains linked to a benzene ring in gelators played a crucial role in the gelation behavior of all compounds in various organic solvents. Longer alkyl chains in molecular skeletons in present gelators are favorable for the gelation of organic solvents. Scanning electron microscope and atomic force microscope observations revealed that the gelator molecules self-assemble into different micro/nanoscale aggregates from a dot, flower, belt, rod, and lamella to wrinkle with change of solvents. Spectral studies indicated that there existed different H-bond formations and hydrophobic forces, depending on the alkyl substituent chains in molecular skeletons. The present work may give some insight to the design and characteristic of new versatile soft materials and potential ECL biosensors with special molecular structures.

Influencing the structure of block copolymer micelles with small molecule additives

NASA Astrophysics Data System (ADS)

Robertson, Megan; Singh, Avantika; Cooksey, Tyler; Kidd, Bryce; Piemonte, Rachele; Wang, Shu; Mai Le, Kim; Madsen, Louis

Amphiphilic block copolymer micelles in water are under broad exploration for drug delivery applications due to their high loading capacity and targeted drug delivery. We aim to understand the kinetic and thermodynamic processes that underlie the self-assembly of diblock copolymer micelle systems. The present work focuses on diblock copolymers containing poly(ethylene oxide) (a hydrophilic polymer) and polycaprolactone (a hydrophobic polymer), which spontaneously self-assemble into spherical micelles in water. Addition of a common good solvent (a co-solvent) for both of the constituting blocks, such as tetrahydrofuran (THF), reduces the interfacial tension at the core-corona interface. We are currently investigating the effect of this phenomenon on the micelle structural properties, using small-angle scattering and nuclear magnetic resonance. We have characterized the hydrodynamic radius, core radius, corona thickness, aggregation number, degree of swelling of the micelle core with the co-solvent, and unimer (free chain) concentration, as a function of the co-solvent concentration. Fundamental knowledge from these studies will inform design of drug delivery systems by allowing us to tailor micelle properties for optimal cargo loading.

A template-free solvent-mediated synthesis of high surface area boron nitride nanosheets for aerobic oxidative desulfurization

DOE PAGES

Wu, Peiwen; Zhu, Wenshuai; Chao, Yanhong; ...

2015-10-16

Hexagonal boron nitride nanosheets (h-BNNs) with rather high specific surface area (SSA) are important two-dimensional layer-structured materials. Here in this study, a solvent-mediated synthesis of h-BNNs revealed a template-free lattice plane control strategy that induced high SSA nanoporous structured h-BNNs with outstanding aerobic oxidative desulfurization performance.

Coordination polymer gels with important environmental and biological applications.

PubMed

Jung, Jong Hwa; Lee, Ji Ha; Silverman, Julian R; John, George

2013-02-07

Coordination Polymer Gels (CPGs) constitute a subset of solid-like metal ion and bridging organic ligand structures (similar to metal-organic frameworks) that form multi-dimensional networks through a trapped solvent as a result of non-covalent interactions. While physical properties of these gels are similar to conventional high molecular weight organic polymer gels, coordination polymer gel systems are often fully reversible and can be assembled and disassembled in the presence of additional energy (heat, sonication, shaking) to give a solution of solvated gelators. Compared to gels resulting from purely organic self-assembled low molecular weight gelators, metal ions incorporated into the fibrilar networks spanning the bulk solvent can impart CPGs with added functionalities. The solid/liquid nature of the gels allows for species to migrate through the gel system and interact with metals, ligands, and the solvent. Chemosensing, catalysis, fluorescence, and drug-delivery applications are some of the many potential uses for these dynamic systems, taking advantage of the metal ion's coordination, the organic polydentate ligand's orientation and functionality, or a combination of these properties. By fine tuning these systems through metal ion and ligand selection and by directing self-assembly with external stimuli the rational synthesis of practical systems can be envisaged.

Supramolecular Complexes Formed by the Self-assembly of Hydrophobic Bis(Zn(2+)-cyclen) Complexes, Copper, and Di- or Triimide Units for the Hydrolysis of Phosphate Mono- and Diesters in Two-Phase Solvent Systems (Cyclen=1,4,7,10-Tetraazacyclododecane).

PubMed

Hisamatsu, Yosuke; Miyazawa, Yuya; Yoneda, Kakeru; Miyauchi, Miki; Zulkefeli, Mohd; Aoki, Shin

2016-01-01

We previously reported on supramolecular complexes 4 and 5, formed by the 4 : 4 : 4 or 2 : 2 : 2 assembly of a dimeric zinc(II) complex (Zn2L(1)) having 2,2'-bipyridyl linker, dianion of cyanuric acid (CA) or 5,5-diethylbarbituric acid (Bar), and copper(II) ion (Cu(2+)) in an aqueous solution. The supermolecule 4 possesses Cu2(μ-OH)2 centers and catalyzes hydrolysis of phosphate monoester dianion, mono(4-nitrophenyl)phosphate (MNP), at neutral pH. In this manuscript, we report on design and synthesis of hydrophobic supermolecules 9 and 10 by 4 : 4 : 4 and 2 : 2 : 2 self-assembly of hydrophobic Zn2L(2) and Zn2L(3) containing long alkyl chains, CA or Bar, and Cu(2+) and their phosphatase activity for the hydrolysis of MNP and bis(4-nitrophenyl)phosphate (BNP) in two-phase solvent systems. We assumed that the Cu2(μ-OH)2 active sites of 9 and 10 would be more stable in organic solvent than in aqueous solution and that product inhibition of the supermolecules might be avoided by the release of HPO4(2-) into the aqueous layer. The findings indicate that 9 and 10 exhibit phosphatase activity in the two-phase solvent system, although catalytic turnover was not observed. Furthermore, the hydrolysis of BNP catalyzed by the hydrophobic 2 : 2 : 2 supermolecules in the two-phase solvent system is described.

Crystallization and Microphase Separation in Chiral Block Copolymers

NASA Astrophysics Data System (ADS)

Ho, Rong-Ming

2012-02-01

Block copolymers composed of chiral entities, denoted as chiral block copolymers (BCP*s), were designed to fabricate helical architectures from self-assembly. A helical phase (denoted H*) was discovered in the self-assembly of poly(styrene)-b-poly(L-lactide) (PS-PLLA) BCPs*. To examine the phase behavior of the PS-PLLA, self-assembled superstructures resulting from the competition between crystallization and microphase separation of the PS-PLLA in solution were examined. A kinetically controlled process by changing non-solvent addition rate was utilized to control the BCP* self-assembly. Single-crystal lozenge lamellae were obtained by the slow self-assembly (i.e., slow non-solvent addition rate) of PS-PLLA whereas amorphous helical ribbon superstructures were obtained from the fast self-assembly (i.e., fast non-solvent addition rate). As a result, the formation of helical architectures from the self-assembly of the PS-PLLA reflects the impact of chirality on microphase separation, but the chiral effect might be overwhelmed by crystallization. Consequently, various crystalline PS-PLLA nanostructures in bulk were obtained by controlling the crystallization temperature of PLLA (Tc,PLLA) at which crystalline helices and crystalline cylinders occur while Tc,PLLA=x Tg,PS, respectively. Anisotropic arrangement of the PLLA crystallites grown within the microdomains was identified. The formation of this exclusive crystalline growth is attributed to the spatial confinement effect for crystallization. While Tc,PLLA=x Tg,PS, the preferential growth may modulate the curvature of microdomains by shifting the molecular chains to access the fast path for crystalline growth due to the increase in chain mobility. As a result, a spring-like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation of helices and to result in crystalline cylinders.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uzun, Suzan; Ilavsky, Jan; Padua, Graciela Wild

Zein, a protein of corn, has an amphiphilic molecule capable of self-assembly into distinctly different structures. In this work, ultra-small-angle X-ray scattering (USAXS) was applied to investigate the formation of self-assembled zein structures in binary solvent systems of ethanol and water. Our study included observing structural changes due to aging. Three hierarchical structures were identified in zein-solvent systems, molecular zein 2D films, believed to be formed by zein rods assembled first into one-dimensional fibers and then into two-dimensional films, and 3D spherical aggregates. Aging did not change the size or shape of primary units, but promoted their self-assembly into intermediatemore » 2D structures and shaped 3D structures into well19 defined spheres. We found that the rheological parameters, consistency index (K) and behavior index (n), storage and loss moduli (G’ and G”) were also measured. K and n, changed markedly with aging, from nearly Newtonian low consistency fresh samples to highly viscous pseudoplastic aged samples. G’ and G” increased with aging for all samples reflecting increased interactions among zein self-assembled structures. Furthermore, viscoelastic parameters indicated that zein dispersions formed gels upon aging. It was observed that USAX reported on molecular scale self-assembly processes, while rheological measurements reported on the macroscale interaction between self-assembled particles. Raman spectra suggested that α-helix to β-sheet transformations prompted zein self-assembly, which influenced the size and morphology of molecular assemblies and ultimately the rheological properties of zein dispersions.« less

Spontaneous Evolution of Nanostructure in Composite Films Consisting of Mixtures of Two Different Block Copolymer Micelles

NASA Astrophysics Data System (ADS)

Kim, Sehee; Char, Kookheon; Sohn, Byeong-Hyeok

2010-03-01

Diblock copolymers consisting of two immiscible polymer blocks covalently bonded together form various self-assembled nanostructures such as spheres, cylinders, and lamellae in bulk phase. In a selective solvent, however, they assemble into micelles with soluble corona brushes and immiscible cores. Both polystyrene-poly(4-vinylpyridine) (PS-b-P4VP) and polystyrene-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymers form micelles with PS coronas and P4VP or P2VP cores in a PS selective solvent (toluene). By varying the mixture ratio between PS-b-P4VP and PS-b-P2VP, composite films based on the micellar mixtures of PS-b-P4VP and PS-b-P2VP were obtained by spin-coating, followed by the solvent annealing with tetrahydrofuran (THF) vapor. Since THF is a solvent for both PS and P2VP blocks and, at the same time, a non-solvent for the P4VP block, PS-P2VP micelles transformed to lamellar multilayers while PS-P4VP micelles remained intact during the THF annealing. The spontaneous evolution of nanostructure in composite films consisting of lamellae layers with BCP micelles were investigated in detail by cross-sectional TEM and AFM.

A Solvent-Vapor Approach toward the Control of Block Ionomer Morphologies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mineart, Kenneth P.; Lee, Byeongdu; Spontak, Richard J.

Sulfonated block ionomers possess advantageous properties for a wide range of diverse applications such as desalination membranes, fuel cells, electroactive media, and photovoltaic devices. Unfortunately, their inherently high incompatibilities and glass transition temperatures e ff ectively prevent the use of thermal annealing, routinely employed to re fi ne the morphologies of nonionic block copolymers. An alternative approach is therefore required to promote morphological equilibration in block ionomers. The present study explores the morphological characteristics of midblock- sulfonated pentablock ionomers (SBIs) di ff ering in their degree of sulfonation (DOS) and cast from solution followed by solvent-vapor annealing (SVA). Transmission electronmore » microscopy con fi rms that fi lms deposited from di ff erent solvent systems form nonequilibrium morphologies due to solvent-regulated self-assembly and drying. A series of SVA tests performed with solvents varying in polarity reveals that exposing cast fi lms to tetrahydrofuran (THF) vapor for at least 2 h constitutes the most e ff ective SVA protocol, yielding the anticipated equilibrium morphology. That is, three SBI grades subjected to THF-SVA self-assemble into well-ordered lamellae wherein the increase in DOS is accompanied by an increase in lamellar periodicity, as measured by small-angle X-ray scattering.« less

Solvent Additive-Assisted Anisotropic Assembly and Enhanced Charge Transport of π-Conjugated Polymer Thin Films.

PubMed

Jeong, Jae Won; Jo, Gyounglyul; Choi, Solip; Kim, Yoong Ahm; Yoon, Hyeonseok; Ryu, Sang-Wan; Jung, Jaehan; Chang, Mincheol

2018-05-30

Charge transport in π-conjugated polymer films involves π-π interactions within or between polymer chains. Here, we demonstrate a facile solution processing strategy that provides enhanced intra- and interchain π-π interactions of the resultant polymer films using a good solvent additive with low volatility. These increased interactions result in enhanced charge transport properties. The effect of the good solvent additive on the intra- and intermolecular interactions, morphologies, and charge transport properties of poly(3-hexylthiophene) (P3HT) films is systematically investigated. We found that the good solvent additive facilitates the self-assembly of P3HT chains into crystalline fibrillar nanostructures by extending the solvent drying time during thin-film formation. As compared to the prior approach using a nonsolvent additive with low volatility, the solvent blend system containing a good solvent additive results in enhanced charge transport in P3HT organic field-effect transistor (OFET) devices [from ca. 1.7 × 10 -2 to ca. 8.2 × 10 -2 cm 2 V -1 s -1 for dichlorobenzene (DCB) versus 4.4 × 10 -2 cm 2 V -1 s -1 for acetonitrile]. The mobility appears to be maximized over a broad spectrum of additive concentrations (1-7 vol %), indicative of a wide processing window. Detailed analysis results regarding the charge injection and transport characteristics of the OFET devices reveal that a high-boiling-point solvent additive decreases both the contact resistance ( R c ) and channel resistance ( R ch ), contributing to the mobility enhancement of the devices. Finally, the platform presented here is proven to be applicable to alternative good solvent additives with low volatility, such as chlorobenzene (CB) and trichlorobenzene (TCB). Specifically, the mobility enhancement of the resultant P3HT films increases in the order CB (bp 131 °C) < DCB (bp 180 °C) < TCB (bp 214 °C), suggesting that solvent additives with higher boiling points provide resultant films with preferable molecular ordering and morphologies for efficient charge transport.

Functional interplay between Mediator and TFIIB in preinitiation complex assembly in relation to promoter architecture

PubMed Central

Eychenne, Thomas; Novikova, Elizaveta; Barrault, Marie-Bénédicte; Alibert, Olivier; Boschiero, Claire; Peixeiro, Nuno; Cornu, David; Redeker, Virginie; Kuras, Laurent; Nicolas, Pierre; Werner, Michel; Soutourina, Julie

2016-01-01

Mediator is a large coregulator complex conserved from yeast to humans and involved in many human diseases, including cancers. Together with general transcription factors, it stimulates preinitiation complex (PIC) formation and activates RNA polymerase II (Pol II) transcription. In this study, we analyzed how Mediator acts in PIC assembly using in vivo, in vitro, and in silico approaches. We revealed an essential function of the Mediator middle module exerted through its Med10 subunit, implicating a key interaction between Mediator and TFIIB. We showed that this Mediator–TFIIB link has a global role on PIC assembly genome-wide. Moreover, the amplitude of Mediator's effect on PIC formation is gene-dependent and is related to the promoter architecture in terms of TATA elements, nucleosome occupancy, and dynamics. This study thus provides mechanistic insights into the coordinated function of Mediator and TFIIB in PIC assembly in different chromatin contexts. PMID:27688401

Characterization of zein assemblies by ultra-small-angle X-ray scattering

DOE PAGES

Uzun, Suzan; Ilavsky, Jan; Padua, Graciela Wild

2017-03-23

Zein, a protein of corn, has an amphiphilic molecule capable of self-assembly into distinctly different structures. In this work, ultra-small-angle X-ray scattering (USAXS) was applied to investigate the formation of self-assembled zein structures in binary solvent systems of ethanol and water. Our study included observing structural changes due to aging. Three hierarchical structures were identified in zein-solvent systems, molecular zein 2D films, believed to be formed by zein rods assembled first into one-dimensional fibers and then into two-dimensional films, and 3D spherical aggregates. Aging did not change the size or shape of primary units, but promoted their self-assembly into intermediatemore » 2D structures and shaped 3D structures into well19 defined spheres. We found that the rheological parameters, consistency index (K) and behavior index (n), storage and loss moduli (G’ and G”) were also measured. K and n, changed markedly with aging, from nearly Newtonian low consistency fresh samples to highly viscous pseudoplastic aged samples. G’ and G” increased with aging for all samples reflecting increased interactions among zein self-assembled structures. Furthermore, viscoelastic parameters indicated that zein dispersions formed gels upon aging. It was observed that USAX reported on molecular scale self-assembly processes, while rheological measurements reported on the macroscale interaction between self-assembled particles. Raman spectra suggested that α-helix to β-sheet transformations prompted zein self-assembly, which influenced the size and morphology of molecular assemblies and ultimately the rheological properties of zein dispersions.« less

Process to prepare stable trifluorostyrene containing compounds grafted to base polymers using a solvent/water mixture

DOEpatents

Roelofs, Mark Gerrit; Yang, Zhen-Yu; Han, Amy Qi

2010-06-15

A fluorinated ion exchange polymer is prepared by grafting at least one grafting monomer derived from trifluorostyrene on to at least one base polymer in a organic solvent/water mixture. These ion exchange polymers are useful in preparing catalyst coated membranes and membrane electrode assemblies used in fuel cells.

Method for distributed object communications based on dynamically acquired and assembled software components

NASA Technical Reports Server (NTRS)

Sundermier, Amy (Inventor)

2002-01-01

A method for acquiring and assembling software components at execution time into a client program, where the components may be acquired from remote networked servers is disclosed. The acquired components are assembled according to knowledge represented within one or more acquired mediating components. A mediating component implements knowledge of an object model. A mediating component uses its implemented object model knowledge, acquired component class information and polymorphism to assemble components into an interacting program at execution time. The interactions or abstract relationships between components in the object model may be implemented by the mediating component as direct invocations or indirect events or software bus exchanges. The acquired components may establish communications with remote servers. The acquired components may also present a user interface representing data to be exchanged with the remote servers. The mediating components may be assembled into layers, allowing arbitrarily complex programs to be constructed at execution time.

Morphology, directed self-assembly and pattern transfer from a high molecular weight polystyrene-block-poly(dimethylsiloxane) block copolymer film

NASA Astrophysics Data System (ADS)

Cheng, Li-Chen; Bai, Wubin; Fernandez Martin, Eduardo; Tu, Kun-Hua; Ntetsikas, Konstantinos; Liontos, George; Avgeropoulos, Apostolos; Ross, C. A.

2017-04-01

The self-assembly of block copolymers with large feature sizes is inherently challenging as the large kinetic barrier arising from chain entanglement of high molecular weight (MW) polymers limits the extent over which long-range ordered microdomains can be achieved. Here, we illustrate the evolution of thin film morphology from a diblock copolymer of polystyrene-block-poly(dimethylsiloxane) exhibiting total number average MW of 123 kg mol-1, and demonstrate the formation of layers of well-ordered cylindrical microdomains under appropriate conditions of binary solvent mix ratio, commensurate film thickness, and solvent vapor annealing time. Directed self-assembly of the block copolymer within lithographically patterned trenches occurs with alignment of cylinders parallel to the sidewalls. Fabrication of ordered cobalt nanowire arrays by pattern transfer was also implemented, and their magnetic properties and domain wall behavior were characterized.

Self-assemblies, helical ribbons and gelation tuned by solvent-gelator interaction in a bi-1,3,4-oxadiazole gelator

NASA Astrophysics Data System (ADS)

Zhao, Chengxiao; Bai, Binglian; Wang, Haitao; Qu, Songnan; Xiao, Guanjun; Tian, Taiji; Li, Min

2013-04-01

A bi-1,3,4-oxadiazole derivative (BOXDH-T12) showed intramolecular charge transition at concentrations lower than 1 × 10-5 mol/L. The self-assembling behaviors of BOXDH-T12 depended on solvents that it self-assembled into H-aggregates in alcohols and slipped packing aggregates in DMSO. FTIR, 1H NMR and TGA results revealed that strong gelator-gelator hydrogen bonding interaction induced H-aggregation of BOXDH-T12 in alcohols and the interactions between DMSO and BOXDH-T12 molecules caused a slipped stacking. BOXDH-T12 can gel the mixtures of DMSO and ethanol through a cooperative effect of the hydrogen bonding, van der Waals interaction and π-π stacking forces, furthermore, helical ribbons could be observed in DMSO/ethanol due to DMSO molecule interacting. In alcohols, solvophobic/solvophilic effect plays a critical role in gelation behaviors.

Microsecond MD Simulations of Nano-patterned Polymer Brushes on Self-Assembled Monolayers

NASA Astrophysics Data System (ADS)

Buie, Creighton; Qiu, Liming; Cheng, Kwan; Park, Soyeun

2010-03-01

Nano-patterned polymer brushes end-grafted onto self-assembled monolayers have gained increasing research interests due to their unique thermodynamic properties and their chemical and biomedical applications in colloids, biosensing and tissue engineering. So far, the interactions between the polymer brushes with the surrounding environments such as the floor and solvent at the nanometer length scale and microsecond time scale are still difficult to obtained experimentally and computationally. Using a Coarse-Grained MD approach, polymer brushes of different monomeric lengths, grafting density and hydrophobicity of the monomers grafted on self-assembled monolayers and in explicit solvent were studied. Molecular level information, such as lateral diffusion, transverse height and volume contour of the brushes, were calculated from our microsecond-MD simulations. Our results demonstrated the significance of the hydration of the polymer in controlling the conformational arrangement of the polymer brushes.

Functional interplay between Mediator and TFIIB in preinitiation complex assembly in relation to promoter architecture.

PubMed

Eychenne, Thomas; Novikova, Elizaveta; Barrault, Marie-Bénédicte; Alibert, Olivier; Boschiero, Claire; Peixeiro, Nuno; Cornu, David; Redeker, Virginie; Kuras, Laurent; Nicolas, Pierre; Werner, Michel; Soutourina, Julie

2016-09-15

Mediator is a large coregulator complex conserved from yeast to humans and involved in many human diseases, including cancers. Together with general transcription factors, it stimulates preinitiation complex (PIC) formation and activates RNA polymerase II (Pol II) transcription. In this study, we analyzed how Mediator acts in PIC assembly using in vivo, in vitro, and in silico approaches. We revealed an essential function of the Mediator middle module exerted through its Med10 subunit, implicating a key interaction between Mediator and TFIIB. We showed that this Mediator-TFIIB link has a global role on PIC assembly genome-wide. Moreover, the amplitude of Mediator's effect on PIC formation is gene-dependent and is related to the promoter architecture in terms of TATA elements, nucleosome occupancy, and dynamics. This study thus provides mechanistic insights into the coordinated function of Mediator and TFIIB in PIC assembly in different chromatin contexts. © 2016 Eychenne et al.; Published by Cold Spring Harbor Laboratory Press.

Supramolecular Assembly of Tripodal Trisamides

NASA Astrophysics Data System (ADS)

Feng, Li

2010-03-01

A series of tripodal trisamide compounds have been synthesized from tris(2-aminoethyl)amine (TREN) by condensation with different acid chlorides. Gelation of organic solvents with these compounds was investigated as a function of concentration and solvent solubility parameter. Compounds made with linear acid chlorides were poor gelators. A gelator made with 2-ethylbutyryl chloride (TREN-EB) was an excellent gelator for many organic solvents. It was found that the minimum gelation concentration of TREN-EB increased with increasing solubility parameter of the solvent. Thin films samples were prepared by spin-coating mixtures of TREN-EB and a poly(acrylate). Scanning force microscopy measurements showed that TREN-EB formed nanofibrillar network structures. In addition a dependence of the network morphology on the casting solvent was found.

Kinetics of presynaptic filament assembly in the presence of single-stranded DNA binding protein and recombination mediator protein.

PubMed

Liu, Jie; Berger, Christopher L; Morrical, Scott W

2013-11-12

Enzymes of the RecA/Rad51 family catalyze DNA strand exchange reactions that are important for homologous recombination and for the accurate repair of DNA double-strand breaks. RecA/Rad51 recombinases are activated by their assembly into presynaptic filaments on single-stranded DNA (ssDNA), a process that is regulated by ssDNA binding protein (SSB) and mediator proteins. Mediator proteins stimulate strand exchange by accelerating the rate-limiting displacement of SSB from ssDNA by the incoming recombinase. The use of mediators is a highly conserved strategy in recombination, but the precise mechanism of mediator activity is unknown. In this study, the well-defined bacteriophage T4 recombination system (UvsX recombinase, Gp32 SSB, and UvsY mediator) is used to examine the kinetics of presynaptic filament assembly on native ssDNA in vitro. Results indicate that the ATP-dependent assembly of UvsX presynaptic filaments on Gp32-covered ssDNA is limited by a salt-sensitive nucleation step in the absence of mediator. Filament nucleation is selectively enhanced and rendered salt-resistant by mediator protein UvsY, which appears to stabilize a prenucleation complex. This mechanism potentially explains how UvsY promotes presynaptic filament assembly at physiologically relevant ionic strengths and Gp32 concentrations. Other data suggest that presynaptic filament assembly involves multiple nucleation events, resulting in many short UvsX-ssDNA filaments or clusters, which may be the relevant form for recombination in vivo. Together, these findings provide the first detailed kinetic model for presynaptic filament assembly involving all three major protein components (recombinase, mediator, and SSB) on native ssDNA.

The Metal Effect on Self-Assembling of Oxalamide Gelators Explored by Mass Spectrometry and DFT Calculations.

PubMed

Dabić, Dario; Brkljačić, Lidija; Tandarić, Tana; Žinić, Mladen; Vianello, Robert; Frkanec, Leo; Kobetić, Renata

2018-01-01

Gels formed by self-assembly of small organic molecules are of wide interest as dynamic soft materials with numerous possible applications, especially in terms of nanotechnology for functional and responsive biomaterials, biosensors, and nanowires. Four bis-oxalamides were chosen to show if electrospray ionization mass spectrometry (ESI-MS) could be used as a prediction of a good gelator and also to shed light on the gelation processes. By inspecting the gelation of several solvent, we showed that bis(amino acid)oxalamide 1 proved to be the most efficient, also being able of forming the largest observable assemblies in the gas phase. The formation of singly charged assemblies holding from one up to six monomer units is the outcome of the strong intermolecular H-bonds, particularly among terminal carboxyl groups. The variation of solvents from polar aprotic towards polar protic did not have any significant effects on the size of the assemblies. The addition of a salt such as NaOAc or Mg(OAc) 2 , depending on the concentration, altered the assembling. Computational analysis at the DFT level aided in the interpretation of the observed trends and revealed that individual gelator molecules spontaneously assemble to higher aggregates, but the presence of the Na + cation disrupts any gelator organization since it becomes significantly more favorable for gelator molecules to bind Na + cations up to the 3:1 ratio than to self-assemble, being fully in line with experimental observations reported here. Graphical Abstract ᅟ.

The Metal Effect on Self-Assembling of Oxalamide Gelators Explored by Mass Spectrometry and DFT Calculations

NASA Astrophysics Data System (ADS)

Dabić, Dario; Brkljačić, Lidija; Tandarić, Tana; Žinić, Mladen; Vianello, Robert; Frkanec, Leo; Kobetić, Renata

2018-01-01

Gels formed by self-assembly of small organic molecules are of wide interest as dynamic soft materials with numerous possible applications, especially in terms of nanotechnology for functional and responsive biomaterials, biosensors, and nanowires. Four bis-oxalamides were chosen to show if electrospray ionization mass spectrometry (ESI-MS) could be used as a prediction of a good gelator and also to shed light on the gelation processes. By inspecting the gelation of several solvent, we showed that bis(amino acid)oxalamide 1 proved to be the most efficient, also being able of forming the largest observable assemblies in the gas phase. The formation of singly charged assemblies holding from one up to six monomer units is the outcome of the strong intermolecular H-bonds, particularly among terminal carboxyl groups. The variation of solvents from polar aprotic towards polar protic did not have any significant effects on the size of the assemblies. The addition of a salt such as NaOAc or Mg(OAc)2, depending on the concentration, altered the assembling. Computational analysis at the DFT level aided in the interpretation of the observed trends and revealed that individual gelator molecules spontaneously assemble to higher aggregates, but the presence of the Na+ cation disrupts any gelator organization since it becomes significantly more favorable for gelator molecules to bind Na+ cations up to the 3:1 ratio than to self-assemble, being fully in line with experimental observations reported here. [Figure not available: see fulltext.

Empirical solvent-mediated potentials hold for both intra-molecular and inter-molecular inter-residue interactions.

PubMed Central

Keskin, O.; Bahar, I.; Badretdinov, A. Y.; Ptitsyn, O. B.; Jernigan, R. L.

1998-01-01

Whether knowledge-based intra-molecular inter-residue potentials are valid to represent inter-molecular interactions taking place at protein-protein interfaces has been questioned in several studies. Differences in the chain connectivity effect and in residue packing geometry between interfaces and single chain monomers have been pointed out as possible sources of distinct energetics for the two cases. In the present study, the interfacial regions of protein-protein complexes are examined to extract inter-molecular inter-residue potentials, using the same statistical methods as those previously adopted for intra-molecular residue pairs. Two sets of energy parameters are derived, corresponding to solvent-mediation and "average residue" mediation. The former set is shown to be highly correlated (correlation coefficient 0.89) with that previously obtained for inter-residue interactions within single chain monomers, while the latter exhibits a weaker correlation (0.69) with its intra-molecular counterpart. In addition to the close similarity of intra- and inter-molecular solvent-mediated potentials, they are shown to be significantly more residue-specific and thereby discriminative compared to the residue-mediated ones, indicating that solvent-mediation plays a major role in controlling the effective inter-residue interactions, either at interfaces, or within single monomers. Based on this observation, a reduced set of energy parameters comprising 20 one-body and 3 two-body terms is proposed (as opposed to the 20 x 20 tables of inter-residue potentials), which reproduces the conventional 20 x 20 tables with a correlation coefficient of 0.99. PMID:9865952

The effect of intermolecular hydrogen bonding on the fluorescence of a bimetallic platinum complex.

PubMed

Zhao, Guang-Jiu; Northrop, Brian H; Han, Ke-Li; Stang, Peter J

2010-09-02

The bimetallic platinum complexes are known as unique building blocks and arewidely utilized in the coordination-driven self-assembly of functionalized supramolecular metallacycles. Hence, photophysical study of the bimetallic platinum complexes will be very helpful for the understanding on the optical properties and further applications of coordination-driven self-assembled supramolecular metallacycles. Herein, we report steady-state and time-resolved spectroscopic experiments as well as quantum chemistry calculations to investigate the significant intermolecular hydrogen bonding effects on the intramolecular charge transfer (ICT) fluorescence of a bimetallic platinum compound 4,4'-bis(trans-Pt(PEt(3))(2)OTf)benzophenone 3 in solution. We demonstrated that the fluorescent state of compound 3 can be assigned as a metal-to-ligand charge transfer (MLCT) state. Moreover, it was observed that the formation of intermolecular hydrogen bonds can effectively lengthen the fluorescence lifetime of 3 in alcoholic solvents compared with that in hexane solvent. At the same time, the electronically excited states of 3 in solution are definitely changed by intermolecular hydrogen bonding interactions. As a consequence, we propose a new fluorescence modulation mechanism by hydrogen bonding to explain different fluorescence emissions of 3 in hydrogen-bonding solvents and nonhydrogen-bonding solvents.

A case-control study of chronic neuropsychiatric disease and organic solvent exposure in automobile assembly plant workers.

PubMed Central

Nelson, N A; Robins, T G; White, R F; Garrison, R P

1994-01-01

A case-control study of chronic neurological and psychiatric disease and occupational exposure to solvents was carried out in eight automobile assembly plants. Cases included 299 subjects who were granted medical disability retirement in 1980-8. Two control groups were selected, the first from those granted retirement in the same period because of medical disability from causes unrelated to solvent exposure. The second included hourly employees from the plant population. In these facilities, solvent exposures tended to be short term and low level, although common: the average duration of exposure was 2.3 years; about 41% experienced at least one day of exposure. Of those exposed, 46% had less than one year of exposure. Results for all psychiatric disease combined (273 cases) suggested that cases had lower exposures than either control group, regardless of how exposure was expressed. Results could not be explained by conventional confounding exposures or characteristics or by usual manifestations of the healthy worker effect. By contrast, chronic neurological disease, and multiple sclerosis in particular, seemed to be associated with exposure, although few cases were identified and observed increases in risk were not statistically significant. PMID:8199679

Solvent-Assisted Surface Engineering for High-Performance All-Inorganic Perovskite Nanocrystal Light-Emitting Diodes.

PubMed

Wang, Lin; Liu, Baiquan; Zhao, Xin; Demir, Hilmi Volkan; Gu, Haoshuang; Sun, Handong

2018-06-13

All-inorganic cesium halide perovskite nanocrystals have attracted much interest in optoelectronic applications for the sake of the readily adjustable band gaps, high photoluminescence quantum yield, pure color emission, and affordable cost. However, because of the ineluctable utilization of organic surfactants during the synthesis, the structural and optical properties of CsPbBr 3 nanocrystals degrade upon transforming from colloidal solutions to solid thin films, which plagues the device operation. Here, we develop a novel solvent-assisted surface engineering strategy, producing high-quality CsPbBr 3 thin films for device applications. A good solvent is first introduced as an assembly trigger to conduct assembly in a one-dimensional direction, which is then interrupted by adding a nonsolvent. The nonsolvent drives the adjacent nanoparticles connecting in a two-dimensional direction. Assembled CsPbBr 3 nanocrystal thin films are densely packed and very smooth with a surface roughness of ∼4.8 nm, which is highly desirable for carrier transport in a light-emitting diode (LED) device. Meanwhile, the film stability is apparently improved. Benefiting from this facile and reliable strategy, we have achieved remarkably improved performance of CsPbBr 3 nanocrystal-based LEDs. Our results not only enrich the methods of nanocrystal surface engineering but also shed light on developing high-performance LEDs.

Clean-in-Place and Reliability Testing of a Commercial 12.5-cm Annular Centrifugal Contactor at the INL

DOE Office of Scientific and Technical Information (OSTI.GOV)

N. R. Mann; T. G. Garn; D. H. Meikrantz

2007-09-01

The renewed interest in advancing nuclear energy has spawned the research of advanced technologies for recycling nuclear fuel. A significant portion of the advanced fuel cycle includes the recovery of selected actinides by solvent extraction methods utilizing centrifugal contactors. Although the use of centrifugal contactors for solvent extraction is widely known, their operation is not without challenges. Solutions generated from spent fuel dissolution contain unknown quantities of undissolved solids. A majority of these solids will be removed via various methods of filtration. However, smaller particles are expected to carry through to downstream solvent extraction processes and equipment. In addition, solids/precipitatesmore » brought about by mechanical or chemical upsets are another potential area of concern. During processing, particulate captured in the rotor assembly by high centrifugal forces eventually forms a cake-like structure on the inner wall introducing balance problems and negatively affecting phase separations. One of the features recently developed for larger engineering scale Annular Centrifugal Contactors (ACCs) is the Clean-In-Place (CIP) capability. Engineered spray nozzles were installed into the hollow central rotor shaft in all four quadrants of the rotor assembly. This arrangement allows for a very convenient and effective method of solids removal from within the rotor assembly.« less

Clean-in-Place and Reliability Testing of a Commercial 12.5 cm Annular Centrifugal Contactor at the INL

DOE Office of Scientific and Technical Information (OSTI.GOV)

N. R. Mann; T. G. Garn; D. H. Meikrantz

2007-09-01

The renewed interest in advancing nuclear energy has spawned the research of advanced technologies for recycling nuclear fuel. A significant portion of the advanced fuel cycle includes the recovery of selected actinides by solvent extraction methods utilizing centrifugal contactors. Although the use of centrifugal contactors for solvent extraction is widely known, their operation is not without challenges. Solutions generated from spent fuel dissolution contain unknown quantities of undissolved solids. A majority of these solids will be removed via various methods of filtration. However, smaller particles are expected to carry through to downstream solvent extraction processes and equipment. In addition, solids/precipitatesmore » brought about by mechanical or chemical upsets are another potential area of concern. During processing, particulate captured in the rotor assembly by high centrifugal forces eventually forms a cake-like structure on the inner wall introducing balance problems and negatively affecting phase separations. One of the features recently developed for larger engineering scale Annular Centrifugal Contactors (ACCs) is the Clean-In-Place (CIP) capability. Engineered spray nozzles were installed into the hollow central rotor shaft in all four quadrants of the rotor assembly. This arrangement allows for a very convenient and effective method of solids removal from within the rotor assembly.« less

Exciplex formation and energy transfer in a self-assembled metal-organic hybrid system.

PubMed

Haldar, Ritesh; Rao, K Venkata; George, Subi J; Maji, Tapas Kumar

2012-05-07

Exciting assemblies: A metal-organic self-assembly of pyrenebutyric acid (PBA), 1,10-phenanthroline (o-phen), and Mg(II) shows solid-state fluorescence originating from a 1:1 PBA-o-phen exciplex. This exciplex fluorescence is sensitized by another residual PBA chromophore through an excited-state energy-transfer process. The solvent polarity modulates the self-assembly and the corresponding exciplex as well as the energy transfer, resulting in tunable emission of the hybrid (see figure). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chiral bis(amino acid)- and bis(amino alcohol)-oxalamide gelators. Gelation properties, self-assembly motifs and chirality effects.

PubMed

Frkanec, Leo; Zinić, Mladen

2010-01-28

Bis(amino acid)- and bis(amino alcohol)oxalamide gelators represent the class of versatile gelators whose gelation ability is a consequence of strong and directional intermolecular hydrogen bonding provided by oxalamide units and lack of molecular symmetry due to the presence of two chiral centres. Bis(amino acid)oxalamides exhibit ambidextrous gelation properties, being capable to form gels with apolar and also highly polar solvent systems and tend to organise into bilayers or inverse bilayers in hydrogel or organic solvent gel assemblies, respectively. (1)H NMR and FTIR studies of gels revealed the importance of the equilibrium between the assembled network and smaller dissolved gelator assemblies. The organisation in gel assemblies deduced from spectroscopic structural studies are in certain cases closely related to organisations found in the crystal structures of selected gelators, confirming similar organisations in gel assemblies and in the solid state. The pure enantiomer/racemate gelation controversy is addressed and the evidence provided that rac-16 forms a stable toluene gel due to resolution into enantiomeric bilayers, which then interact giving gel fibres and a network of different morphology compared to its (S,S)-enantiomer gel. The TEM investigation of both gels confirmed distinctly different gel morphologies, which allowed the relationship between the stereochemical form of the gelator, the fibre and the network morphology and the network solvent immobilisation capacity to be proposed. Mixing of the constitutionally different bis(amino acid) and bis(amino alcohol)oxalamide gelators resulted in some cases in highly improved gelation efficiency denoted as synergic gelation effect (SGE), being highly dependent also on the stereochemistry of the component gelators. Examples of photo-induced gelation based on closely related bis(amino acid)-maleic acid amide and -fumaramide and stilbene derived oxalamides where gels form by irradiation of the solution of a non-gelling isomer and its photo-isomerisation into gelling isomer are provided, as well as examples of luminescent gels, gel-based fluoride sensors, LC-gels and nanoparticle-hydrogel composites.

Stoichiometric sensing to opt between gelation and crystallization.

PubMed

Vidyasagar, Adiyala; Sureshan, Kana M

2015-10-05

A new class of organogelators having a cyclohexane-1a,3a-diol motif capable of congealing non-polar liquids was developed. These gelators underwent crystallization at low concentration and gelation above the critical gelation concentration (CGC) in the same solvent. The crystals and gel fibers were analyzed by single crystal XRD and PXRD respectively, which revealed their different modes of assembly. The XRD studies and thermogravimetric analysis (TGA) confirmed that the crystals contain a water of crystallization whereas the gel fibers do not. A systematic study revealed that when the concentration of the gelator exceeds that of adventitious water in the solvent, it congeals the solvent and when the concentration of the gelator is less than water, it undergoes crystallization. This unprecedented stoichiometric sensing behavior in deciding the mode of self-assembly offers a handle to opt between mutually competing gelation and crystallization. We have confirmed that the system can be biased to congeal or crystallize by varying the amount of water. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Atomistic simulation of hydrophobin HFBII conformation in aqueous and fluorous media and at the water/vacuum interface.

PubMed

Raffaini, Giuseppina; Milani, Roberto; Ganazzoli, Fabio; Resnati, Giuseppe; Metrangolo, Pierangelo

2016-01-01

Hydrophobins are proteins of interest for numerous applications thanks to their unique conformational and surface properties and their ability to self-assemble at interfaces. Here we report fully atomistic molecular mechanics and molecular dynamics results together with circular dichroism experimental data, aimed to study the conformational properties of the hydrophobin HFBII in a fluorinated solvent in comparison with a water solution and/or at an aqueous/vacuum interface. Both the atomistic simulations and the circular dichroism data show the remarkable structural stability of HFBII at all scales in all these environments, with no significant structural change, although a small cavity is formed in the fluorinated solvent. The combination of theoretical calculations and circular dichroism data can describe in detail the protein conformation and flexibility in different solvents and/or at an interface, and constitutes a first step towards the study of their self-assembly. Copyright © 2015 Elsevier Inc. All rights reserved.

Symmetry Breaking in the Supramolecular Gels of an Achiral Gelator Exclusively Driven by π-π Stacking.

PubMed

Shen, Zhaocun; Jiang, Yuqian; Wang, Tianyu; Liu, Minghua

2015-12-30

Supramolecular symmetry breaking, in which chiral assemblies with imbalanced right- and left-handedness emerge from achiral molecular building blocks, has been achieved in the organogels of a C3-symmetric molecule only via π-π stacking. Specifically, an achiral C3-symmetric benzene-1,3,5-tricarboxylate substituted with methyl cinnamate through ester bond was found to form organogels in various organic solvents. More interestingly, when gels formed in cyclohexane, symmetry breaking occurred; i.e., optically active organogels together with the helical nanofibers with predominant handedness were obtained. Furthermore, the stochastically appeared imbalanced helicity could be driven to desired handedness by utilizing slight chiral solvents such as (R)- or (S)-terpinen-4-ol. Remarkably, the handedness of supramolecular assemblies thus formed could be kept even when the chiral solvents were removed. For the first time, we show that symmetry breaking can occur in supramolecular gel system driven exclusively through π-π stacking.

Direct Assembly of Modified Proteins on Carbon Nanotubes in an Aqueous Solution

NASA Technical Reports Server (NTRS)

Kim, Jae-Woo; Lillehei, Peter T.; Park, Cheol; Harrison, Joycelyn S.

2007-01-01

Carbon nanotubes (CNTs) have superior mechanical and electrical properties that have opened up many potential applications. However, poor dispersibility and solubility, due to the substantial van der Waals attraction between tubes, have prevented the use of CNTs in practical applications, especially biotechnology applications. Effective dispersion of CNTs into small bundles or individual tubes in solvents is crucial to ensure homogeneous properties and enable practical applications. In addition to dispersion of CNTs into a solvent, the selection of appropriate solvent, which is compatible with a desired matrix, is an important factor to improve the mechanical, thermal, optical, and electrical properties of CNT-based fibers and composites. In particular, dispersion of CNTs into an aqueous system has been a challenge due to the hydrophobic nature of CNTs. Here we show an effective method for dispersion of both single wall CNTs (SWCNTs) and few wall CNTs (FWCNTs) in an aqueous buffer solution. We also show an assembly of cationized Pt-cored ferritins on the well dispersed CNTs in an aqueous buffer solution.

Docking glycosaminoglycans to proteins: analysis of solvent inclusion

NASA Astrophysics Data System (ADS)

Samsonov, Sergey A.; Teyra, Joan; Pisabarro, M. Teresa

2011-05-01

Glycosaminoglycans (GAGs) are anionic polysaccharides, which participate in key processes in the extracellular matrix by interactions with protein targets. Due to their charged nature, accurate consideration of electrostatic and water-mediated interactions is indispensable for understanding GAGs binding properties. However, solvent is often overlooked in molecular recognition studies. Here we analyze the abundance of solvent in GAG-protein interfaces and investigate the challenges of adding explicit solvent in GAG-protein docking experiments. We observe PDB GAG-protein interfaces being significantly more hydrated than protein-protein interfaces. Furthermore, by applying molecular dynamics approaches we estimate that about half of GAG-protein interactions are water-mediated. With a dataset of eleven GAG-protein complexes we analyze how solvent inclusion affects Autodock 3, eHiTs, MOE and FlexX docking. We develop an approach to de novo place explicit solvent into the binding site prior to docking, which uses the GRID program to predict positions of waters and to locate possible areas of solvent displacement upon ligand binding. To investigate how solvent placement affects docking performance, we compare these results with those obtained by taking into account information about the solvent position in the crystal structure. In general, we observe that inclusion of solvent improves the results obtained with these methods. Our data show that Autodock 3 performs best, though it experiences difficulties to quantitatively reproduce experimental data on specificity of heparin/heparan sulfate disaccharides binding to IL-8. Our work highlights the current challenges of introducing solvent in protein-GAGs recognition studies, which is crucial for exploiting the full potential of these molecules for rational engineering.

Solvent induced modifications to fiber nanostructure and morphology for 12HSA molecular gels

NASA Astrophysics Data System (ADS)

Gao, Jie

Molecular organogels are thermo reversible quasi-solid materials, which are formed by low molecular weight organogelators (LMOGs) undergoing supramolecular aggregation via non-covalent interactions, forming a three-dimensional fibrillar network. Numerous applications of molecular organogels are been investigated as edible oils, drug release matrices and personal care products. The chemistry of the organic phase (i.e., solvent) influences every level of structure in organogels. Different solvents induce LMOG to assemble into "crystal like" fibers, which have more than one crystal form, lamellar arrangement and domain size. Differences in these solid states are known to affect the macroscopic properties of the gel, including critical gelator concentration (CGC), melting point, melting enthalpy and opacity.12-hydroxystearic acid (12HSA) was examined in several classes of organic solvents with different function groups. These gels, sols or precipitates were analyzed using a series of techniques including: powder x-ray diffraction (XRD), differential scanning calorimetry (DSC), fourier-transform infrared spectroscopy (FT-IR), pulsed nuclear magnetic resonance spectroscopy (pNMR) and microscopy. Specifically, certain solvents caused 12HSA to self-assemble into a triclinic parallel polymorphic form with subcell spacing of ~4.6, 3.9, and 3.8 A and an interdigitated unit cell with a lamellar arrangement (38~44 A). This polymorphic form corresponded to a less effective sphereultic supramolecular crystalline network, which immobilizes solvents at CGC greater than 1.5 wt %. The other group of solvents induce a hexagonal subcell spacing (i.e., unit sub cell spacing ~4.1 A) and are arranged in a multi lamellar fashion with a unit cell greater than the bimolecular length of 12HSA (~54 A).This polymorphic form corresponds to fibrillar aggregates with a CGC less than 1 wt %.

Crops: a green approach toward self-assembled soft materials.

PubMed

Vemula, Praveen Kumar; John, George

2008-06-01

To date, a wide range of industrial materials such as solvents, fuels, synthetic fibers, and chemical products are being manufactured from petroleum resources. However, rapid depletion of fossil and petroleum resources is encouraging current and future chemists to orient their research toward designing safer chemicals, products, and processes from renewable feedstock with an increased awareness of environmental and industrial impact. Advances in genetics, biotechnology, process chemistry, and engineering are leading to a new manufacturing concept for converting renewable biomass to valuable fuels and products, generally known as the biorefinery concept. The swift integration of crop-based materials synthesis and biorefinery manufacturing technologies offers the potential for new advances in sustainable energy alternatives and biomaterials that will lead to a new manufacturing paradigm. This Account presents a novel and emerging concept of generating various forms of soft materials from crops (an alternate feedstock). In future research, developing biobased soft materials will be a fascinating yet demanding practice, which will have direct impact on industrial applications as an economically viable alternative. Here we discuss some remarkable examples of glycolipids generated from industrial byproducts such as cashew nut shell liquid, which upon self-assembly produced soft nanoarchitectures including lipid nanotubes, twisted/helical nanofibers, low-molecular-weight gels, and liquid crystals. Synthetic methods applied to a "chiral pool" of carbohydrates using the selectivity of enzyme catalysis yield amphiphilic products derived from biobased feedstock including amygdalin, trehalose, and vitamin C. This has been achieved with a lipase-mediated regioselective synthetic procedure to obtain such amphiphiles in quantitative yields. Amygdalin amphiphiles showed unique gelation behavior in a broad range of solvents such as nonpolar hexanes to polar aqueous solutions. Importantly, an enzyme triggered drug-delivery model for hydrophobic drugs was demonstrated by using these supramolecularly assembled hydrogels. Following a similar biocatalytic approach, vitamin C amphiphiles were synthesized with different hydrocarbon chain lengths, and their ability to self-assemble into molecular gels and liquid crystals has been studied in detail. Such biobased soft materials were successfully used to develop novel organic-inorganic hybrid materials by in situ synthesis of metal nanoparticles. The self-assembled soft materials were characterized by several spectroscopic techniques, UV-visible, infrared, and fluorescence spectrophotometers, as well as microscopic methods including polarized optical, confocal, scanning, and transmission electron microscopes, and thermal analysis. The molecular packing of the hierarchically assembled bilayer membranes was fully elucidated by X-ray analysis. We envision that the results summarized in this Account will encourage interdisciplinary collaboration between scientists in the fields of organic synthesis, soft materials research, and green chemistry to develop functional materials from underutilized crop-based renewable feedstock, with innovation driven both by material needs and environmentally benign design principles.

Simultaneously 'pushing' and 'pulling' graphene oxide into low-polar solvents through a designed interface.

PubMed

Liu, Zhen; Liu, Jingquan; Wang, Yichao; Razal, Joselito M; Francis, Paul S; Biggs, Mark J; Barrow, Colin J; Yang, Wenrong

2018-08-03

Dispersing graphene oxide (GO) in low-polar solvents can realize a perfect self-assembly with functional molecules and application in removal of organic impurities that only dissolve in low-polar solvents. The surface chemistry of GO plays an important role in its dispersity in these solvents. The direct transfer of hydrophilic GO into low-polar solvents, however, has remained an experimental challenge. In this study, we design an interface to transfer GO by simultaneously 'pushing and pulling' the nanosheets into low-polar solvents. Our approach is outstanding due to the ability to obtain monolayers of chemically reduced GO (CRGO) with designed surface properties in the organic phase. Using the transferred GO or CRGO dispersions, we have fabricated GO/fullerene nanocomposites and assessed the ability of CRGOs for dye adsorption. We hope our work can provide a universal approach for the phase transfer of other nanomaterials.

Behaviour of a solvent trapped in a physical molecular gel

NASA Astrophysics Data System (ADS)

Morfin, I.; Spagnoli, S.; Rambaud, C.; Longeville, S.; Plazanet, M.

2016-03-01

Physical gels formed by amphiphilic molecules, namely in this study Methyl-4,6-O-benzylidene-? -D-mannopyranoside, can be form either in polar and protic liquid-like water or in organic apolar solvent such as toluene. The solvent, that influences the supramolecular organization of the gelators, plays an important role in the stability and formation of the gel phase. Gelator-solvent interactions govern not only the assembly but also the solvent diffusion in the material. We present here measurements of neutron scattering (Time of Flight and Neutron Spin Echo) characterizing this microscopic behaviour. In addition, we show that transient grating spectroscopy provides valuable information through the characterization of the longitudinal acoustic wave propagating in the system. Opposite effects on the speed of sound in the gels are observed for the two solvents investigated, being relevant of the interactions between the gelators and the surrounding liquid.

Star-like supramolecular polymers fabricated by a Keplerate cluster with cationic terminated polymers and their self-assembly into vesicles.

PubMed

Zhang, Qian; He, Lipeng; Wang, Hui; Zhang, Cheng; Liu, Weisheng; Bu, Weifeng

2012-07-18

The electrostatic combination of a Keplerate cluster, [Mo(132)O(372)(CH(3)COO)(30)(H(2)O)(72)](42-) with cationic terminated poly(styrene) yields polyoxometalate-based supramolecular star polymers, which can further self-assemble into vesicular aggregates in CHCl(3)-MeOH mixed solvent.

Theoretical aspects of self-assembly of proteins: A Kirkwood-Buff-theory approach

NASA Astrophysics Data System (ADS)

Ben-Naim, Arieh

2013-06-01

A new approach to the problem of self-assembly of proteins induced by temperature, pressure, or changes in solute concentration is presented. The problem is formulated in terms of Le Chatelier principle, and a solution is sought in terms of the Kirkwood-Buff theory of solutions. In this article we focus on the pressure and solute effects on the association-dissociation equilibrium. We examine the role of both hydrophobic and hydrophilic effects. We argue that the latter are more important than the former. The solute effect, on the other hand, depends on the preferential solvation of the monomer and the aggregate with respect to solvent and co-solvent molecules. An experimental approach based on model compounds to study these effects is suggested.

Theoretical aspects of self-assembly of proteins: a Kirkwood-Buff-theory approach.

PubMed

Ben-Naim, Arieh

2013-06-14

A new approach to the problem of self-assembly of proteins induced by temperature, pressure, or changes in solute concentration is presented. The problem is formulated in terms of Le Chatelier principle, and a solution is sought in terms of the Kirkwood-Buff theory of solutions. In this article we focus on the pressure and solute effects on the association-dissociation equilibrium. We examine the role of both hydrophobic and hydrophilic effects. We argue that the latter are more important than the former. The solute effect, on the other hand, depends on the preferential solvation of the monomer and the aggregate with respect to solvent and co-solvent molecules. An experimental approach based on model compounds to study these effects is suggested.

Chaperonin GroEL Reassembly: An Effect of Protein Ligands and Solvent Composition

PubMed Central

Ryabova, Nataliya; Marchenkov, Victor; Kotova, Nina; Semisotnov, Gennady

2014-01-01

Chaperonin GroEL is a complex oligomeric heat shock protein (Hsp60) assisting the correct folding and assembly of other proteins in the cell. An intriguing question is how GroEL folds itself. According to the literature, GroEL reassembly is dependent on chaperonin ligands and solvent composition. Here we demonstrate dependence of GroEL reassembly efficiency on concentrations of the essential factors (Mg2+, ADP, ATP, GroES, ammonium sulfate, NaCl and glycerol). Besides, kinetics of GroEL oligomerization in various conditions was monitored by the light scattering technique and proved to be two-exponential, which suggested accumulation of a certain oligomeric intermediate. This intermediate was resolved as a heptamer by nondenaturing blue electrophoresis of GroEL monomers during their assembly in the presence of both Mg-ATP and co-chaperonin GroES. Presumably, this intermediate heptamer plays a key role in formation of the GroEL tetradecameric particle. The role of co-chaperonin GroES (Hsp10) in GroEL assembly is also discussed. PMID:24970225

Process for recycling components of a PEM fuel cell membrane electrode assembly

DOEpatents

Shore, Lawrence [Edison, NJ

2012-02-28

The membrane electrode assembly (MEA) of a PEM fuel cell can be recycled by contacting the MEA with a lower alkyl alcohol solvent which separates the membrane from the anode and cathode layers of the assembly. The resulting solution containing both the polymer membrane and supported noble metal catalysts can be heated under mild conditions to disperse the polymer membrane as particles and the supported noble metal catalysts and polymer membrane particles separated by known filtration means.

Role for the MED21-MED7 Hinge in Assembly of the Mediator-RNA Polymerase II Holoenzyme*

PubMed Central

Sato, Shigeo; Tomomori-Sato, Chieri; Tsai, Kuang-Lei; Yu, Xiaodi; Sardiu, Mihaela; Saraf, Anita; Washburn, Michael P.; Florens, Laurence; Asturias, Francisco J.; Conaway, Ronald C.

2016-01-01

Mediator plays an integral role in activation of RNA polymerase II (Pol II) transcription. A key step in activation is binding of Mediator to Pol II to form the Mediator-Pol II holoenzyme. Here, we exploit a combination of biochemistry and macromolecular EM to investigate holoenzyme assembly. We identify a subset of human Mediator head module subunits that bind Pol II independent of other subunits and thus probably contribute to a major Pol II binding site. In addition, we show that binding of human Mediator to Pol II depends on the integrity of a conserved “hinge” in the middle module MED21-MED7 heterodimer. Point mutations in the hinge region leave core Mediator intact but lead to increased disorder of the middle module and markedly reduced affinity for Pol II. These findings highlight the importance of Mediator conformation for holoenzyme assembly. PMID:27821593

Interfacial solvation thermodynamics

NASA Astrophysics Data System (ADS)

Ben-Amotz, Dor

2016-10-01

Previous studies have reached conflicting conclusions regarding the interplay of cavity formation, polarizability, desolvation, and surface capillary waves in driving the interfacial adsorptions of ions and molecules at air-water interfaces. Here we revisit these questions by combining exact potential distribution results with linear response theory and other physically motivated approximations. The results highlight both exact and approximate compensation relations pertaining to direct (solute-solvent) and indirect (solvent-solvent) contributions to adsorption thermodynamics, of relevance to solvation at air-water interfaces, as well as a broader class of processes linked to the mean force potential between ions, molecules, nanoparticles, proteins, and biological assemblies.

Solvent-Free Self-Assembly to the Synthesis of Nitrogen-Doped Ordered Mesoporous Polymers for Highly Selective Capture and Conversion of CO2.

PubMed

Liu, Fujian; Huang, Kuan; Wu, Qin; Dai, Sheng

2017-07-01

A solvent-free induced self-assembly technology for the synthesis of nitrogen-doped ordered mesoporous polymers (N-OMPs) is developed, which is realized by mixing polymer precursors with block copolymer templates, curing at 140-180 °C, and calcination to remove the templates. This synthetic strategy represents a significant advancement in the preparation of functional porous polymers through a fast and scalable yet environmentally friendly route, since no solvents or catalysts are used. The synthesized N-OMPs and their derived catalysts are found to exhibit competitive CO 2 capacities (0.67-0.91 mmol g -1 at 25 °C and 0.15 bar), extraordinary CO 2 /N 2 selectivities (98-205 at 25 °C), and excellent activities for catalyzing conversion of CO 2 into cyclic carbonate (conversion >95% at 100 °C and 1.2 MPa for 1.5 h). The solvent-free technology developed in this work can also be extended to the synthesis of N-OMP/SiO 2 nanocomposites, mesoporous SiO 2 , crystalline mesoporous TiO 2 , and TiPO, demonstrating its wide applicability in porous material synthesis. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Polymeric assembly of gluten proteins in an aqueous ethanol solvent.

PubMed

Dahesh, Mohsen; Banc, Amélie; Duri, Agnès; Morel, Marie-Hélène; Ramos, Laurence

2014-09-25

The supramolecular organization of wheat gluten proteins is largely unknown due to the intrinsic complexity of this family of proteins and their insolubility in water. We fractionate gluten in a water/ethanol mixture (50/50 v/v) and obtain a protein extract which is depleted in gliadin, the monomeric part of wheat gluten proteins, and enriched in glutenin, the polymeric part of wheat gluten proteins. We investigate the structure of the proteins in the solvent used for extraction over a wide range of concentration, by combining X-ray scattering and multiangle static and dynamic light scattering. Our data show that, in the ethanol/water mixture, the proteins display features characteristic of flexible polymer chains in a good solvent. In the dilute regime, the proteins form very loose structures of characteristic size 150 nm, with an internal dynamics which is quantitatively similar to that of branched polymer coils. In more concentrated regimes, data highlight a hierarchical structure with one characteristic length scale of the order of a few nm, which displays the scaling with concentration expected for a semidilute polymer in good solvent, and a fractal arrangement at a much larger length scale. This structure is strikingly similar to that of polymeric gels, thus providing some factual knowledge to rationalize the viscoelastic properties of wheat gluten proteins and their assemblies.

Structural Transformation of Li-Excess Cathode Materials via Facile Preparation and Assembly of Sonication-Induced Colloidal Nanocrystals for Enhanced Lithium Storage Performance.

PubMed

Zhao, Jianqing; Huang, Ruiming; Ramos, Pablo; Yue, Yiying; Wu, Qinglin; Pavanello, Michele; Zhou, Jieyu; Kuai, Xiaoxiao; Gao, Lijun; He, Huixin; Wang, Ying

2017-09-13

A surfactant-free sonication-induced route is developed to facilely prepare colloidal nanocrystals of Li-excess layered Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 (marked as LMNCO) material. The sonication process plays a critical role in forming LMNCO nanocrystals in ethanol (ethanol molecules marked as EtOHs) and inducing the interaction between LMNCO and solvent molecules. The formation mechanism of LMNCO-EtOH supramolecules in the colloidal dispersion system is proposed and examined by the theoretical simulation and light scattering technique. It is suggested that the as-formed supramolecule is composed of numerous ethanol molecules capping the surface of the LMNCO nanocrystal core via hydrogen bonding. Such chemisorption gives rise to dielectric polarization of the absorbed ethanol molecules, resulting in a negative surface charge of LMNCO colloids. The self-assembly behaviors of colloidal LMNCO nanocrystals are then tentatively investigated by tuning the solvent evaporation condition, which results in diverse superstructures of LMNCO materials after the evaporation of ethanol. The reassembled LMNCO architectures exhibit remarkably improved capacity and cyclability in comparison with the original LMNCO particles, demonstrating a very promising cathode material for high-energy lithium-ion batteries. This work thus provides new insights into the formation and self-assembly of multiple-element complex inorganic colloids in common and surfactant-free solvents for enhanced performance in device applications.

Exciplex fluorescence emission from simple organic intramolecular constructs in non-polar and highly polar media as model systems for DNA-assembled exciplex detectors.

PubMed

Bichenkova, Elena V; Sardarian, Ali R; Wilton, Amanda N; Bonnet, Pascal; Bryce, Richard A; Douglas, Kenneth T

2006-01-21

Organic intramolecular exciplexes, N-(4-dimethylaminobenzyl)-N-(1-pyrenemethyl)amine (1) and N'-4-dimethylaminonaphthyl-N-(1-pyrenemethyl)amine (2), were used as model systems to reveal major factors affecting their exciplex fluorescence, and thus lay the basis for developing emissive target-assembled exciplexes for DNA-mounted systems in solution. These models with an aromatic pyrenyl hydrocarbon moiety as an electron acceptor appropriately connected to an aromatic dimethylamino electron donor component (N,N-dimethylaminophenyl or N,N-dimethylaminonaphthyl) showed strong intramolecular exciplex emission in both non-polar and highly polar solvents. The effect of dielectric constant on the maximum wavelength for exciplex emission was studied, and emission was observed for 1 and 2 over the full range of solvent from non-polar hydrocarbons up to N-methylformamide with a dielectric constant of 182. Quantum yields were determined for these intramolecular exciplexes in a range of solvents relative to that for Hoechst 33,258. Conformational analysis of 1 was performed both computationally and via qualitative 2D NMR using (1)H-NOESY experiments. The results obtained indicated the contribution of pre-folded conformation(s) to the ground state of 1 conducive to exciplex emission. This research provides the initial background for design of self-assembled, DNA-mounted exciplexes and underpins further development of exciplex-based hybridisation bioassays.

Unique organogel formation with macroporous materials constructed by the freeze-drying of aqueous cyclodextrin solutions.

PubMed

Marui, Yasuhiro; Kikuzawa, Akira; Kida, Toshiyuki; Akashi, Mitsuru

2010-07-06

Macroporous cyclodextrin materials (MP-alpha-, beta-, and gamma-CDs) were easily fabricated by the freeze-drying of aqueous solutions of alpha-, beta-, and gamma-CDs. These MP-CDs showed the absorption ability toward various organic solvents and oils to give organogels at ambient temperature. The morphological changes of the MP-CD microstructures were observed through the absorption of organic solvents. In particular, the absorption of polar organic solvents with hydrogen-bond forming ability, including 1,4-dioxane and ethanol, by the MP-CDs caused remarkable morphological changes in the microstructures. The absorption of these polar solvents by MP-alpha- and gamma-CDs resulted in the formation of channel-type assemblies of alpha- and gamma-CDs, respectively.

Mesoscale Simulation and Machine Learning of Asphaltene Aggregation Phase Behavior and Molecular Assembly Landscapes.

PubMed

Wang, Jiang; Gayatri, Mohit A; Ferguson, Andrew L

2017-05-11

Asphaltenes constitute the heaviest fraction of the aromatic group in crude oil. Aggregation and precipitation of asphaltenes during petroleum processing costs the petroleum industry billions of dollars each year due to downtime and production inefficiencies. Asphaltene aggregation proceeds via a hierarchical self-assembly process that is well-described by the Yen-Mullins model. Nevertheless, the microscopic details of the emergent cluster morphologies and their relative stability under different processing conditions remain poorly understood. We perform coarse-grained molecular dynamics simulations of a prototypical asphaltene molecule to establish a phase diagram mapping the self-assembled morphologies as a function of temperature, pressure, and n-heptane:toluene solvent ratio informing how to control asphaltene aggregation by regulating external processing conditions. We then combine our simulations with graph matching and nonlinear manifold learning to determine low-dimensional free energy surfaces governing asphaltene self-assembly. In doing so, we introduce a variant of diffusion maps designed to handle data sets with large local density variations, and report the first application of many-body diffusion maps to molecular self-assembly to recover a pseudo-1D free energy landscape. Increasing pressure only weakly affects the landscape, serving only to destabilize the largest aggregates. Increasing temperature and toluene solvent fraction stabilizes small cluster sizes and loose bonding arrangements. Although the underlying molecular mechanisms differ, the strikingly similar effect of these variables on the free energy landscape suggests that toluene acts upon asphaltene self-assembly as an effective temperature.

Optoelectronic functional materials based on alkylated-π molecules: self-assembled architectures and nonassembled liquids.

PubMed

Li, Hongguang; Choi, Jiyoung; Nakanishi, Takashi

2013-05-07

The engineering of single molecules into higher-order hierarchical assemblies is a current research focus in molecular materials chemistry. Molecules containing π-conjugated units are an important class of building blocks because their self-assembly is not only of fundamental interest, but also the key to fabricating functional systems for organic electronic and photovoltaic applications. Functionalizing the π-cores with "alkyl chains" is a common strategy in the molecular design that can give the system desirable properties, such as good solubility in organic solvents for solution processing. Moreover, the alkylated-π system can regulate the self-assembly behavior by fine-tuning the intermolecular forces. The optimally assembled structures can then exhibit advanced functions. However, while some general rules have been revealed, a comprehensive understanding of the function played by the attached alkyl chains is still lacking, and current methodology is system-specific in many cases. Better clarification of this issue requires contributions from carefully designed libraries of alkylated-π molecular systems in both self-assembly and nonassembly materialization strategies. Here, based on recent efforts toward this goal, we show the power of the alkyl chains in controlling the self-assembly of soft molecular materials and their resulting optoelectronic properties. The design of alkylated-C60 is selected from our recent research achievements, as the most attractive example of such alkylated-π systems. Some other closely related systems composed of alkyl chains and π-units are also reviewed to indicate the universality of the methodology. Finally, as a contrast to the self-assembled molecular materials, nonassembled, solvent-free, novel functional liquid materials are discussed. In doing so, a new journey toward the ultimate organic "soft" materials is introduced, based on alkylated-π molecular design.

Recognition-Mediated Assembly of Quantum Dot Polymer Conjugates with Controlled Morphology

PubMed Central

Nandwana, Vikas; Subramani, Chandramouleeswaran; Eymur, Serkan; Yeh, Yi-Cheun; Tonga, Gulen Yesilbag; Tonga, Murat; Jeong, Youngdo; Yang, Boqian; Barnes, Michael D.; Cooke, Graeme; Rotello, Vincent M.

2011-01-01

We have demonstrated a polymer mediated “bricks and mortar” method for the self-assembly of quantum dots (QDs). This strategy allows QDs to self-assemble into structured aggregates using complementary three-point hydrogen bonding. The resulting nanocomposites have distinct morphologies and inter-particle distances based on the ratio between QDs and polymer. Time resolved photoluminescence measurements showed that the optical properties of the QDs were retained after self-assembly. PMID:22016664

DNAzyme-Based Logic Gate-Mediated DNA Self-Assembly.

PubMed

Zhang, Cheng; Yang, Jing; Jiang, Shuoxing; Liu, Yan; Yan, Hao

2016-01-13

Controlling DNA self-assembly processes using rationally designed logic gates is a major goal of DNA-based nanotechnology and programming. Such controls could facilitate the hierarchical engineering of complex nanopatterns responding to various molecular triggers or inputs. Here, we demonstrate the use of a series of DNAzyme-based logic gates to control DNA tile self-assembly onto a prescribed DNA origami frame. Logic systems such as "YES," "OR," "AND," and "logic switch" are implemented based on DNAzyme-mediated tile recognition with the DNA origami frame. DNAzyme is designed to play two roles: (1) as an intermediate messenger to motivate downstream reactions and (2) as a final trigger to report fluorescent signals, enabling information relay between the DNA origami-framed tile assembly and fluorescent signaling. The results of this study demonstrate the plausibility of DNAzyme-mediated hierarchical self-assembly and provide new tools for generating dynamic and responsive self-assembly systems.

Solubility Limits in Lennard-Jones Mixtures: Effects of Disparate Molecule Geometries.

PubMed

Dyer, Kippi M; Perkyns, John S; Pettitt, B Montgomery

2015-07-23

In order to better understand general effects of the size and energy disparities between macromolecules and solvent molecules in solution, especially for macromolecular constructs self-assembled from smaller molecules, we use the first- and second-order exact bridge diagram extensions of the HNC integral equation theory to investigate single-component, binary, ternary, and quaternary mixtures of Lennard-Jones fluids. For pure fluids, we find that the HNCH3 bridge function integral equation (i.e., exact to third order in density) is necessary to quantitatively predict the pure gas and pure liquid sides of the coexistence region of the phase diagram of the Lennard-Jones fluid. For the mixtures, we find that the HNCH2 bridge function integral equation is sufficient to qualitatively predict solubility in the binary, ternary, and quaternary mixtures, up to the nominal solubility limit. The results, as limiting cases, should be useful to several problems, including accurate phase diagram predictions for complex mixtures, design of self-assembling nanostructures via solvent controls, and the solvent contributions to the conformational behavior of macromolecules in complex fluids.

Role for the MED21-MED7 Hinge in Assembly of the Mediator-RNA Polymerase II Holoenzyme.

PubMed

Sato, Shigeo; Tomomori-Sato, Chieri; Tsai, Kuang-Lei; Yu, Xiaodi; Sardiu, Mihaela; Saraf, Anita; Washburn, Michael P; Florens, Laurence; Asturias, Francisco J; Conaway, Ronald C; Conaway, Joan W

2016-12-23

Mediator plays an integral role in activation of RNA polymerase II (Pol II) transcription. A key step in activation is binding of Mediator to Pol II to form the Mediator-Pol II holoenzyme. Here, we exploit a combination of biochemistry and macromolecular EM to investigate holoenzyme assembly. We identify a subset of human Mediator head module subunits that bind Pol II independent of other subunits and thus probably contribute to a major Pol II binding site. In addition, we show that binding of human Mediator to Pol II depends on the integrity of a conserved "hinge" in the middle module MED21-MED7 heterodimer. Point mutations in the hinge region leave core Mediator intact but lead to increased disorder of the middle module and markedly reduced affinity for Pol II. These findings highlight the importance of Mediator conformation for holoenzyme assembly. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

The High-Resolution Structure of Activated Opsin Reveals a Conserved Solvent Network in the Transmembrane Region Essential for Activation.

PubMed

Blankenship, Elise; Vahedi-Faridi, Ardeschir; Lodowski, David T

2015-12-01

Rhodopsin, a light-activated G protein coupled receptor (GPCR), has been the subject of numerous biochemical and structural investigations, serving as a model receptor for GPCRs and their activation. We present the 2.3-Å resolution structure of native source rhodopsin stabilized in a conformation competent for G protein binding. An extensive water-mediated hydrogen bond network linking the chromophore binding site to the site of G protein binding is observed, providing connections to conserved motifs essential for GPCR activation. Comparison of this extensive solvent-mediated hydrogen-bonding network with the positions of ordered solvent in earlier crystallographic structures of rhodopsin photointermediates reveals both static structural and dynamic functional water-protein interactions present during the activation process. When considered along with observations that solvent occupies similar positions in the structures of other GPCRs, these analyses strongly support an integral role for this dynamic ordered water network in both rhodopsin and GPCR activation. Copyright © 2015 Elsevier Ltd. All rights reserved.

The Role of Solvent-Solute Interactions on The Behavior of Low Molecular Mass Organo-Gelators

NASA Astrophysics Data System (ADS)

Cavicchi, Kevin; Feng, Li

2012-02-01

Low molecular mass organo-gelators (LMOGs) are a class of small molecules that can self-assemble in organic solvents to form three-dimensional fibrillar networks. This has a profound effect on the viscoelastic properties of the solution causing physical gelation. These gels have uses in a range of industries including cosmetics, foodstuffs, plastics, petroleum and pharmaceuticals. A fundamental question in this field is: What makes a good LMOG? This talk will discuss the relationships between the viscoelastic properties and thermodynamic phase behavior of LMOG/solvent solutions. The regular solution model was used to fit the liquidus line and sol/gel transition temperature vs. concentration in different solvents to determine LMOG-solvent interaction parameters (χ = A/T). This parameter A was found to scale with the solubility parameter of the solvent, especially for non-polar solvents. This demonstrates that gelation is strongly linked to LMOG solubility and indicates that the bulk thermodynamic parameters of the LMOG (solubility parameter and melting temperature) are useful to predict the solution behavior of LMOGs.

Synthesis and characterization of gold nanodogbones by the seeded mediated growth method

NASA Astrophysics Data System (ADS)

Huang, Chien-Jung; Chiu, Pin-Hsiang; Wang, Yeong-Her; Meen, Teen-Hang; Yang, Cheng-Fu

2007-10-01

Novel gold nanodogbones (GDBs) are successfully fabricated using a simple seeded mediated growth (SMG) method. The shapes of GDBs depend on the amount of added vitamin C solvent. The amount of vitamin C solvent was varied from 10 to 40 µl to investigate the influence of vitamin C solvent on the GDBs. It is found that the aspect ratios (R) of GDBs were in the range from 2.34 to 1.46, and the UV-vis absorption measurement revealed a pronounced blueshift on the longitudinal surface plasmon resonance (SPR) band from 713 to 676 nm. The GDBs were determined by x-ray diffraction (XRD) to be single-crystalline with a face-centered cubic (fcc) structure. The lattice constant calculated from this selected-area electron diffraction (SAED) pattern is 4.068 Å.

Persistent Self-Association of Solute Molecules in Solution.

PubMed

Tang, Weiwei; Mo, Huaping; Zhang, Mingtao; Parkin, Sean; Gong, Junbo; Wang, Jingkang; Li, Tonglei

2017-11-02

The structural evolvement of a solute determines the crystallization outcome. The self-association mechanism leading to nucleation, however, remains poorly understood. Our current study explored the solution chemistry of a model compound, tolfenamic acid (TFA), in three different solvents mainly by solution NMR. It was found that hydrogen-bonded pairs of solute-solute or solute-solvent stack with each through forming a much weaker π-π interaction as the concentration increases. Depending on the solvent, configurations of the solution species may be retained in the resultant crystal structure or undergo rearrangement. Yet, the π-π stacking is always retained in the crystal regardless of the solvent used for the crystallization. The finding suggests that nucleation not only involves the primary intermolecular interaction (hydrogen bonding) but also engages the secondary forces in the self-assembly process.

Influence of polar solvents on photovoltaic performance of Monascusred dye-sensitized solar cell

NASA Astrophysics Data System (ADS)

Lee, Jae Wook; Kim, Tae Young; Ko, Hyun Seok; Han, Shin; Lee, Suk-Ho; Park, Kyung Hee

Dye-sensitized solar cells (DSSCs) were assembled using natural dyes extracted from Monascus red pigment as a sensitizer. In this work, we studied the adsorption characteristics for harvesting sunlight and the electrochemical behavior for electron transfer in Monascus red DSSC using different solvents. The effect of polar aprotic and protic solvents including water, ethanol, and dimethylsulfoxide (DMSO) used in the sensitization process was investigated for the improvement in conversion efficiency of a cell. As for the Monascus red dye-sensitized electrode in DMSO solvent, the solar cell yields a short-circuit current density (Jsc) of 1.23 mA/cm2, a photovoltage (Voc) of 0.75 V, and a fill factor of 0.72, corresponding to an energy conversion efficiency (η) of 0.66%.

Effect of solvent quality on aggregate structures of common surfactants.

PubMed

Hollamby, Martin J; Tabor, Rico; Mutch, Kevin J; Trickett, Kieran; Eastoe, Julian; Heenan, Richard K; Grillo, Isabelle

2008-11-04

Aggregate structures of two model surfactants, AOT and C12E5 are studied in pure solvents D2O, dioxane-d8 (d-diox) and cyclohexane-d12 (C6D12) as well as in formulated D2O/d-diox and d-diox/C6D12 mixtures. As such these solvents and mixtures span a wide and continuous range of polarities. Small-angle neutron scattering (SANS) has been employed to follow an evolution of the preferred aggregate curvature, from normal micelles in high polarity solvents, through to reversed micelles in low polarity media. SANS has also been used to elucidate the micellar size, shape as well as to highlight intermicellar interactions. The results shed new light on the nature of aggregation structures in intermediate polarity solvents, and point to a region of solvent quality (as characterized by Hildebrand Solubility Parameter, Snyder polarity parameter or dielectric constant) in which aggregation is not favored. Finally these observed trends in aggregation as a function of solvent quality are successfully used to predict the self-assembly behavior of C12E5 in a different solvent, hexane-d14 (C6D14).

Low molecular weight oligomers of amyloid peptides display β-barrel conformations: A replica exchange molecular dynamics study in explicit solvent

NASA Astrophysics Data System (ADS)

De Simone, Alfonso; Derreumaux, Philippe

2010-04-01

The self-assembly of proteins and peptides into amyloid fibrils is connected to over 40 pathological conditions including neurodegenerative diseases and systemic amyloidosis. Diffusible, low molecular weight protein and peptide oligomers that form in the early steps of aggregation appear to be the harmful cytotoxic species in the molecular etiology of these diseases. So far, the structural characterization of these oligomers has remained elusive owing to their transient and dynamic features. We here address, by means of full atomistic replica exchange molecular dynamics simulations, the energy landscape of heptamers of the amyloidogenic peptide NHVTLSQ from the beta-2 microglobulin protein. The simulations totaling 5 μs show that low molecular weight oligomers in explicit solvent consist of β-barrels in equilibrium with amorphous states and fibril-like assemblies. The results, also accounting for the influence of the pH on the conformational properties, provide a strong evidence of the formation of transient β-barrel assemblies in the early aggregation steps of amyloid-forming systems. Our findings are discussed in terms of oligomers cytotoxicity.

Vibrational energy transfer between carbon nanotubes and nonaqueous solvents: a molecular dynamics study.

PubMed

Nelson, Tammie R; Chaban, Vitaly V; Prezhdo, Victor V; Prezhdo, Oleg V

2011-05-12

We report molecular dynamics (MD) simulation of energy exchange between single-walled carbon nanotubes (CNTs) and two aprotic solvents, acetonitrile and cyclohexane. Following our earlier study of hydrated CNTs, we find that the time scales and molecular mechanisms of the energy transfer are largely independent of the nature of the surrounding medium, and therefore, should hold for other media including polymer matrices and DNA. The vibrational energy exchange between CNT and solvents exhibits two time-scales. Over half of the energy is transferred in less than one picosecond, indicating that the dominant exchange mechanism is inertial relaxation. It occurs by collisions of solvent molecules with CNT walls, facilitated by the short-range Lennard-Jones interaction. Additional several picoseconds are required for the remainder of the vibrational energy exchange, corresponding to the diffusive relaxation mechanism and involving collective molecular motions. The faster stage of the CNT-solvent energy exchange occurs on the same time-scale, and therefore, competes with the vibrational energy relaxation inside CNTs. The energy exchange time-scales are significantly influenced by the arrangement of solvent molecules inside CNTs. Generally, the effects of confinement on the dynamics can be rationalized by analysis of the solvent structure. For the same CNT diameter, the extent of the confinement effect strongly depends on the size of the solvent molecules. Icelike properties in water seen in small CNTs disappear in CNTs with intermediate diameters. In acetonitrile and cyclohexane, medium size CNTs still show strong confinement effects. Rotational motions of acetonitrile molecules are inhibited, and the cyclohexane density is dramatically decreased. The disbalance between the local temperatures of the inside and outside regions of the solvent equilibrates through a tube-mediated interaction, rather than by a direct coupling between the two solvent subsystems. In all cases, the CNT-solvent energy transfer is mediated by slow motions in the frequency range of CNT radial breathing modes.

Emulsion Solvent Evaporation-Induced Self-Assembly of Block Copolymers Containing pH-Sensitive Block.

PubMed

Wu, Yuqing; Wang, Ke; Tan, Haiying; Xu, Jiangping; Zhu, Jintao

2017-09-26

A simple yet efficient method is developed to manipulate the self-assembly of pH-sensitive block copolymers (BCPs) confined in emulsion droplets. Addition of acid induces significant variation in morphological transition (e.g., structure and surface composition changes) of the polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) assemblies, due to the hydrophobic-hydrophilic transition of the pH-sensitive P4VP block via protonation. In the case of pH > pKa (P4VP) (pKa (P4VP) = 4.8), the BCPs can self-assemble into pupa-like particles because of the nearly neutral wetting of PS and P4VP blocks at the oil/water interface. As expected, onion-like particles obtained when pH is slightly lower than pKa (P4VP) (e.g., pH = 3.00), due to the interfacial affinity to the weakly hydrophilic P4VP block. Interestingly, when pH was further decreased to ∼2.5, interfacial instability of the emulsion droplets was observed, and each emulsion droplet generated nanoscale assemblies including vesicles, worm-like and/or spherical micelles rather than a nanostructured microparticle. Furthermore, homopolymer with different molecular weights and addition ratio are employed to adjust the interactions among copolymer blocks. By this means, particles with hierarchical structures can be obtained. Moreover, owing to the kinetically controlled processing, we found that temperature and stirring speed, which can significantly affect the kinetics of the evaporation of organic solvent and the formation of particles, played a key role in the morphology of the assemblies. We believe that manipulation of the property for the aqueous phase is a promising strategy to rationally design and fabricate polymeric assemblies with desirable shapes and internal structures.

Membrane-mediated interaction between retroviral capsids

NASA Astrophysics Data System (ADS)

Zhang, Rui; Nguyen, Toan

2012-02-01

A retrovirus is an RNA virus that is replicated through a unique strategy of reverse transcription. Unlike regular enveloped viruses which are assembled inside the host cells, the assembly of retroviral capsids happens right on the cell membrane. During the assembly process, the partially formed capsids deform the membrane, giving rise to an elastic energy. When two such partial capsids approach each other, this elastic energy changes. Or in other words, the two partial capsids interact with each other via the membrane. This membrane mediated interaction between partial capsids plays an important role in the kinetics of the assembly process. In this work, this membrane mediated interaction is calculated both analytically and numerically. It is worth noting that the diferential equation determining the membrane shape in general nonlinear and cannot be solved analytically,except in the linear region of small deformations. And it is exactly the nonlinear regime that is important for the assembly kinetics of retroviruses as it provides a large energy barrier. The theory developed here is applicable to more generic cases of membrane mediated interactions between two membrane-embedded proteins.

Tuning Molecular Weights of Bombyx mori (B. mori) Silk Sericin to Modify Its Assembly Structures and Materials Formation

PubMed Central

2015-01-01

Bombyx mori (B. mori) silk sericin is a protein with features desirable as a biomaterial, such as increased hydrophilicity and biodegradation, as well as resistance to oxidation, bacteria, and ultraviolet light. In contrast to other widely studied B. mori silk proteins such as fibroin, sericin is still unexplored as a building block for fabricating biomaterial, and thus a facile technique of processing it into a material is needed. Here, electrospinning technology was used to fabricate it into biomaterials from two forms of B. mori silk sericin with different molecular weights, one is a low (12.0 kDa) molecular sericin (LS) form and another is a high (66.0 kDa) molecular weight sericin (HS) form. Circular dichroism (CD) spectra showed that LS in hexafluoroacetone (HFA) solvent adopted a predominantly random coil conformation, whereas HS tended to form a β-sheet structure along with a large content of random coils. In addition, LS and HS in HFA solvent were found to form cylinder-like smaller nanoparticles and larger irregular aggregates before electrospinning, respectively. As a result, biomaterials based on microparticles and nanofibers were successfully fabricated by electrospinning of LS and HS dissolved in HFA, respectively. The cell viability and differentiation assay indicated that nanofibers and microparticles improved cell adhesion, growth, and differentiation, proving that the scaffolds electrospun from sericin are biocompatible regardless of its molecular weight. The microparticles, not common in electrospinning of silk proteins reported previously, were found to promote the osteogenic differentiation of mesenchymal stem cells in comparison to the nanofibers. This study suggested that molecular weight of sericin mediates its secondary structure and assembly structure, which in turn leads to a control of final morphology of the electrospun materials. The microparticles and nanofibers of sericin can be potentially used as building blocks for fabricating the scaffolds for tissue engineering. PMID:25050697

Tuning molecular weights of Bombyx mori (B. mori) silk sericin to modify its assembly structures and materials formation.

PubMed

Yang, Mingying; Shuai, Yajun; Zhou, Guanshan; Mandal, Namita; Zhu, Liangjun; Mao, Chuanbin

2014-08-27

Bombyx mori (B. mori) silk sericin is a protein with features desirable as a biomaterial, such as increased hydrophilicity and biodegradation, as well as resistance to oxidation, bacteria, and ultraviolet light. In contrast to other widely studied B. mori silk proteins such as fibroin, sericin is still unexplored as a building block for fabricating biomaterial, and thus a facile technique of processing it into a material is needed. Here, electrospinning technology was used to fabricate it into biomaterials from two forms of B. mori silk sericin with different molecular weights, one is a low (12.0 kDa) molecular sericin (LS) form and another is a high (66.0 kDa) molecular weight sericin (HS) form. Circular dichroism (CD) spectra showed that LS in hexafluoroacetone (HFA) solvent adopted a predominantly random coil conformation, whereas HS tended to form a β-sheet structure along with a large content of random coils. In addition, LS and HS in HFA solvent were found to form cylinder-like smaller nanoparticles and larger irregular aggregates before electrospinning, respectively. As a result, biomaterials based on microparticles and nanofibers were successfully fabricated by electrospinning of LS and HS dissolved in HFA, respectively. The cell viability and differentiation assay indicated that nanofibers and microparticles improved cell adhesion, growth, and differentiation, proving that the scaffolds electrospun from sericin are biocompatible regardless of its molecular weight. The microparticles, not common in electrospinning of silk proteins reported previously, were found to promote the osteogenic differentiation of mesenchymal stem cells in comparison to the nanofibers. This study suggested that molecular weight of sericin mediates its secondary structure and assembly structure, which in turn leads to a control of final morphology of the electrospun materials. The microparticles and nanofibers of sericin can be potentially used as building blocks for fabricating the scaffolds for tissue engineering.

Dimensional control of block copolymer nanofibers with a π-conjugated core: crystallization-driven solution self-assembly of amphiphilic poly(3-hexylthiophene)-b-poly(2-vinylpyridine).

PubMed

Gwyther, Jessica; Gilroy, Joe B; Rupar, Paul A; Lunn, David J; Kynaston, Emily; Patra, Sanjib K; Whittell, George R; Winnik, Mitchell A; Manners, Ian

2013-07-08

With the aim of accessing colloidally stable, fiberlike, π-conjugated nanostructures of controlled length, we have studied the solution self-assembly of two asymmetric crystalline-coil, regioregular poly(3-hexylthiophene)-b-poly(2-vinylpyridine) (P3HT-b-P2VP) diblock copolymers, P3HT23-b-P2VP115 (block ratio=1:5) and P3HT44-b-P2VP115 (block ratio=ca. 1:3). The self-assembly studies were performed under a variety of solvent conditions that were selective for the P2VP block. The block copolymers were prepared by using Cu-catalyzed azide-alkyne cycloaddition reactions of azide-terminated P2VP and alkyne end-functionalized P3HT homopolymers. When the block copolymers were self-assembled in a solution of a 50% (v/v) mixture of THF (a good solvent for both blocks) and an alcohol (a selective solvent for the P2VP block) by means of the slow evaporation of the common solvent; fiberlike micelles with a P3HT core and a P2VP corona were observed by transmission electron microscopy (TEM). The average lengths of the micelles were found to increase as the length of the hydrocarbon chain increased in the P2VP-selective alcoholic solvent (MeOH3 μm) fiberlike micelles were prepared by the dialysis of solutions of the block copolymers in THF against iPrOH. Furthermore the widths of the fibers were dependent on the degree of polymerization of the chain-extended P3HT blocks. The crystallinity and π-conjugated nature of the P3HT core in the fiberlike micelles was confirmed by a combination of UV/Vis spectroscopy, photoluminescence (PL) measurements, and wide-angle X-ray scattering (WAXS). Intense sonication (iPrOH, 1 h, 0 °C) of the fiberlike micelles formed by P3HT23-b-P2VP115 resulted in small (ca. 25 nm long) stublike fragments that were subsequently used as initiators in seeded growth experiments. Addition of P3HT23-b-P2VP115 unimers to the seeds allowed the preparation of fiberlike micelles with narrow length distributions (L(w)/L(n) < 1.11) and lengths from about 100-300 nm, that were dependent on the unimer-to-seed micelle ratio. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Static Electricity-Responsive Supramolecular Assembly.

PubMed

Jintoku, Hirokuni; Ihara, Hirotaka; Matsuzawa, Yoko; Kihara, Hideyuki

2017-12-01

Stimuli-responsive materials can convert between molecular scale and macroscopic scale phenomena. Two macroscopic static electricity-responsive phenomena based on nanoscale supramolecular assemblies of a zinc porphyrin derivative are presented. One example involves the movement of supramolecular assemblies in response to static electricity. The assembly of a pyridine (Py) complex of the above-mentioned derivative in cyclohexane is drawn to a positively charged material, whereas the assembly of a 3,5-dimethylpyridine complex is drawn to a negatively charged material. The second phenomenon involves the movement of a non-polar solvent in response to static electrical stimulation. A cyclohexane solution containing a small quantity of the Py-complexed assembly exhibited a strong movement response towards negatively charged materials. Based on spectroscopic measurements and electron microscope observations, it was revealed that the assembled formation generates the observed response to static electricity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Bottom-up view of water network-mediated CO2 reduction using cryogenic cluster ion spectroscopy and direct dynamics simulations.

PubMed

Breen, Kristin J; DeBlase, Andrew F; Guasco, Timothy L; Voora, Vamsee K; Jordan, Kenneth D; Nagata, Takashi; Johnson, Mark A

2012-01-26

The transition states of a chemical reaction in solution are generally accessed through exchange of thermal energy between the solvent and the reactants. As such, an ensemble of reacting systems approaches the transition state configuration of reactant and surrounding solvent in an incoherent manner that does not lend itself to direct experimental observation. Here we describe how gas-phase cluster chemistry can provide a detailed picture of the microscopic mechanics at play when a network of six water molecules mediates the trapping of a highly reactive "hydrated electron" onto a neutral CO(2) molecule to form a radical anion. The exothermic reaction is triggered from a metastable intermediate by selective excitation of either the reactant CO(2) or the water network, which is evidenced by the evaporative decomposition of the product cluster. Ab initio molecular dynamics simulations of energized CO(2)·(H(2)O)(6)(-) clusters are used to elucidate the nature of the network deformations that mediate intracluster electron capture, thus revealing the detailed solvent fluctuations implicit in the Marcus theory for electron-transfer kinetics in solution.

Molecular modeling of directed self-assembly of block copolymers: Fundamental studies of processing conditions and evolutionary pattern design

NASA Astrophysics Data System (ADS)

Khaira, Gurdaman Singh

Rapid progress in the semi-conductor industry has pushed for smaller feature sizes on integrated electronic circuits. Current photo-lithographic techniques for nanofabrication have reached their technical limit and are problematic when printing features small enough to meet future industrial requirements. "Bottom-up'' techniques, such as the directed self-assembly (DSA) of block copolymers (BCP), are the primary contenders to compliment current "top-down'' photo-lithography ones. For industrial requirements, the defect density from DSA needs to be less than 1 defect per 10 cm by 10 cm. Knowledge of both material synthesis and the thermodynamics of the self-assembly process are required before optimal operating conditions can be found to produce results adequate for industry. The work present in this thesis is divided into three chapters, each discussing various aspects of DSA as studied via a molecular model that contains the essential physics of BCP self-assembly. Though there are various types of guiding fields that can be used to direct BCPs over large wafer areas with minimum defects, this study focuses only on chemically patterned substrates. The first chapter addresses optimal pattern design by describing a framework where molecular simulations of various complexities are coupled with an advanced optimization technique to find a pattern that directs a target morphology. It demonstrates the first ever study where BCP self-assembly on a patterned substrate is optimized using a three-dimensional description of the block-copolymers. For problems pertaining to DSA, the methodology is shown to converge much faster than the traditional random search approach. The second chapter discusses the metrology of BCP thin films using TEM tomography and X-ray scattering techniques, such as CDSAXS and GISAXS. X-ray scattering has the advantage of being able to quickly probe the average structure of BCP morphologies over large wafer areas; however, deducing the BCP morphology from the information in inverse space is a challenging task. Using the optimization techniques and molecular simulations discussed in the first chapter, a methodology to reconstruct BCP morphology from X-ray scattering data is described. It is shown that only a handful of simulation parameters that come directly from experiment are able to describe the morphologies observed from real X-ray scattering experiments. The last chapter focuses on the use of solvents to assist the self-assembly of BCPs. Additional functionality to capture the process of solvent annealing is also discussed. The bulk behavior of solvated mixtures of BCPs with solvents of various affinities is described, and the results are consistent with the experimentally observed behavior of BCPs in the presence of solvents.

The Role of Interfacial Water in Protein-Ligand Binding: Insights from the Indirect Solvent Mediated Potential of Mean Force.

PubMed

Cui, Di; Zhang, Bin W; Matubayasi, Nobuyuki; Levy, Ronald M

2018-02-13

Classical density functional theory (DFT) can be used to relate the thermodynamic properties of solutions to the indirect solvent mediated part of the solute-solvent potential of mean force (PMF). Standard, but powerful numerical methods can be used to estimate the solute-solvent PMF from which the indirect part can be extracted. In this work we show how knowledge of the direct and indirect parts of the solute-solvent PMF for water at the interface of a protein receptor can be used to gain insights about how to design tighter binding ligands. As we show, the indirect part of the solute-solvent PMF is equal to the sum of the 1-body (energy + entropy) terms in the inhomogeneous solvation theory (IST) expansion of the solvation free energy. To illustrate the effect of displacing interfacial water molecules with particular direct/indirect PMF signatures on the binding of ligands, we carry out simulations of protein binding with several pairs of congeneric ligands. We show that interfacial water locations that contribute favorably or unfavorably at the 1-body level (energy + entropy) to the solvation free energy of the solute can be targeted as part of the ligand design process. Water locations where the indirect PMF is larger in magnitude provide better targets for displacement when adding a functional group to a ligand core.

A toxic organic solvent-free technology for the preparation of PEGylated paclitaxel nanosuspension based on human serum albumin for effective cancer therapy

PubMed Central

Yin, Tingjie; Dong, Lihui; Cui, Bei; Wang, Lei; Yin, Lifang; Zhou, Jianping; Huo, Meirong

2015-01-01

Clinically, paclitaxel (PTX) is one of most commonly prescribed therapies against a wide range of solid neoplasms. Despite its success, the clinical applicability of PTX (Taxol®) is severely hampered by systemic toxicities induced by Cremophor EL. While attempts to bypass the need for Cremophor EL have been developed through platforms such as Abraxane™, nab™ relies heavily on the use of organic solvents, namely, chloroform. The toxicity introduced by residual chloroform poses a potential risk to patient health. To mitigate the toxicities of toxic organic solvent-based manufacture methods, we have designed a method for the formulation of PTX nanosuspensions (PTX-PEG [polyethylene glycol]-HSA [human serum albumin]) that eliminates the dependence on toxic organic solvents. Coined the solid-dispersion technology, this technique permits the dispersion of PTX into PEG skeleton without the use of organic solvents or Cremophor EL as a solubilizer. Once the PTX-PEG dispersion is complete, the dispersion can be formulated with HSA into nanosuspensions suitable for intravenous administration. Additionally, the incorporation of PEG permits the prolonged circulation through the steric stabilization effect. Finally, HSA-mediated targeting permits active receptor-mediated endocytosis for enhanced tumor uptake and reduced side effects. By eliminating the need for both Cremophor EL and organic solvents while simultaneously increasing antitumor efficacy, this method provides a superior alternative to currently accepted methods for PTX delivery. PMID:26715846

Influence of polar solvents on photovoltaic performance of Monascusred dye-sensitized solar cell.

PubMed

Lee, Jae Wook; Kim, Tae Young; Ko, Hyun Seok; Han, Shin; Lee, Suk-Ho; Park, Kyung Hee

2014-05-21

Dye-sensitized solar cells (DSSCs) were assembled using natural dyes extracted from Monascus red pigment as a sensitizer. In this work, we studied the adsorption characteristics for harvesting sunlight and the electrochemical behavior for electron transfer in Monascus red DSSC using different solvents. The effect of polar aprotic and protic solvents including water, ethanol, and dimethylsulfoxide (DMSO) used in the sensitization process was investigated for the improvement in conversion efficiency of a cell. As for the Monascus red dye-sensitized electrode in DMSO solvent, the solar cell yields a short-circuit current density (Jsc) of 1.23mA/cm(2), a photovoltage (Voc) of 0.75V, and a fill factor of 0.72, corresponding to an energy conversion efficiency (η) of 0.66%. Copyright © 2014 Elsevier B.V. All rights reserved.

Morphogenesis of polycrystalline dendritic patterns from evaporation of a reactive nanofluid sessile drop

NASA Astrophysics Data System (ADS)

Wu, Hua; Briscoe, Wuge H.

2018-04-01

We report polycrystalline residual patterns with dendritic micromorphologies upon fast evaporation of a mixed-solvent sessile drop containing reactive ZnO nanoparticles. The molecular and particulate species generated in situ upon evaporative drying collude with and modify the Marangoni solvent flows and Bénard-Marangoni instabilities, as they undergo self-assembly and self-organization under conditions far from equilibrium, leading to the ultimate hierarchical central cellular patterns surrounded by a peripheral coffee ring upon drying.

Peptide-directed self-assembly of hydrogels

PubMed Central

Kopeček, Jindřich; Yang, Jiyuan

2009-01-01

This review focuses on the self-assembly of macromolecules mediated by the biorecognition of peptide/protein domains. Structures forming α-helices and β-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

Role of solvents on the oxygen reduction and evolution of rechargeable Li-O2 battery

NASA Astrophysics Data System (ADS)

Christy, Maria; Arul, Anupriya; Zahoor, Awan; Moon, Kwang Uk; Oh, Mi Young; Stephan, A. Manuel; Nahm, Kee Suk

2017-02-01

The choice of electrolyte solvent is expected to play a key role in influencing the lithium-oxygen battery performance. The electrochemical performances of three electrolytes composed of lithium bis (trifluoromethane sulfonyl) imide (LiTFSI) salt and different solvents namely, ethylene carbonate/propylene carbonate (EC/PC), tetra ethylene glycol dimethyl ether (TEGDME) and dimethyl sulfoxide (DMSO) are investigated by assembling lithium oxygen cells. The electrolyte composition significantly varied the specific capacity of the battery. The choice of electrolyte also influences the overpotential, cycle life, and rechargeability of the battery. Electrochemical impedance spectra, cyclic voltammetry, and chronoamperometry were utilized to determine the reversible reactions associated with the air cathode.

Highχ block copolymers for directed self-assembly patterning without the need for topcoat or solvent annealing

NASA Astrophysics Data System (ADS)

Xu, Kui; Hockey, Mary Ann; Calderas, Eric; Guerrero, Douglas; Sweat, Daniel; Fiehler, Jeffrey

2017-03-01

High-χ block copolymers for directed self-assembly (DSA) patterning that do not need topcoat or solvent annealing have been developed. A variety of functionalities have been successfully added into the block copolymers, such as balanced surface energy between the polymer blocks, outstandingly high χ, tunable glass transition temperature (Tg), and selective crosslinking. Perpendicular orientation control, as desired for patterning, of the block copolymers can be simply achieved by thermal annealing due to the equal surface energy of the polymer blocks at the annealing temperatures, which allows avoiding solvent annealing or top-coat. The χ value can be tuned up to achieve L0 as low as 8-10 nm for lamellar-structured block copolymers and hole/pillar size as small as 5-6 nm for cylinder-structured block copolymers. The Tg of the block copolymers can be tuned to improve the kinetics of thermal annealing by enhancing the polymer chain mobility. Block-selective crosslinking facilitates the pattern transfer by mitigating pattern collapse during wet etching and improving oxygen plasma etching selectivity between the polymer blocks. This paper provides an introductory review of our high-χ block copolymer materials with various functionalities for achieving improved DSA performance.

Time-Dependent Solid State Polymorphism of a Series of Donor-Acceptor Dyads

PubMed Central

Peebles, Cameron; Alvey, Paul M.; Lynch, Vincent; Iverson, Brent L.

2014-01-01

In order to exploit the use of favorable electrostatic interactions between aromatic units in directing the assembly of donor-acceptor (D-A) dyads, the present work examines the ability of conjugated aromatic D-A dyads with symmetric side chains to exhibit solid-state polymorphism as a function of time during the solid formation process. Four such dyads were synthesized and their packing in the solid-state from either slower (10-20 days) or faster (1-2 days) evaporation from solvent was investigated using single crystal X-ray analysis and powder X-ray diffraction. Two of the dyads exhibited tail-to-tail (A-A) packing upon slower evaporation from solvent and head-to-tail (D-A) packing upon faster evaporation from solvent. A combination of single crystal analysis and XRD patterns were used to create models wherein a packing model for the other two dyads is proposed. Our findings suggest that while side chain interactions in asymmetric aromatic dyads can play an important role in enforcing segregated D-A dyad assembly, slowly evaporating symmetrically substituted aromatic dyads allows for favorable electrostatic interactions between the aromatic moieties to facilitate the organization of the dyads in the solid-state. PMID:24678269

Effects of Immersion Solvent on Photovoltaic and Photophysical Properties of Porphyrin-Sensitized Solar Cells.

PubMed

Hayashi, Hironobu; Higashino, Tomohiro; Kinjo, Yuriko; Fujimori, Yamato; Kurotobi, Kei; Chabera, Pavel; Sundström, Villy; Isoda, Seiji; Imahori, Hiroshi

2015-08-26

Memory effects in self-assembled monolayers (SAMs) of zinc porphyrin carboxylic acid on TiO2 electrodes have been demonstrated for the first time by evaluating the photovoltaic and electron transfer properties of porphyrin-sensitized solar cells prepared by using different immersion solvents sequentially. The structure of the SAM of the porphyrin on the TiO2 was maintained even after treating the porphyrin monolayer with different neat immersion solvents (memory effect), whereas it was altered by treatment with solutions containing different porphyrins (inverse memory effect). Infrared spectroscopy shows that the porphyrins in the SAM on the TiO2 could be exchanged with the same or analogous porphyrin, leading to a change in the structure of the porphyrin SAM. The memory and inverse memory effects are well correlated with a change in porphyrin geometry, mainly the tilt angle of the porphyrin along the long molecular axis from the surface normal on the TiO2, as well as with kinetics of electron transfer between the porphyrin and TiO2. Such a new structure-function relationship for DSSCs will be very useful for the rational design and optimization of photoelectrochemical and photovoltaic properties of molecular assemblies on semiconductor surfaces.

Self-assembling Structures and Sol-Gel Transition of Optically Active and Racemic 12-Hydroxystearic Acids in Organic Solvents

NASA Astrophysics Data System (ADS)

Takeno, Hiroyuki; Mochizuki, Tomomitsu; Yoshiba, Kazuto; Kondo, Shingo; Dobashi, Toshiaki

Self-assembling structures and sol-gel transition in solution of optically active and racemic 12-Hydroxystearic acids (HSA) have been investigated by means of small-angle X-ray scattering (SAXS), differential scanning calorimetry and rheological measurements. Apparently two kinds of gel, transparent gel and turbid gel were obtained in different solvents or by changing concentrations in the same solvent. The melting temperature of the turbid gel is higher than that of the transparent gel. The difference can be qualitatively explained by the dissolution of the crystals (melting point depression) in non-ideal solutions. The SAXS profiles of the transparent gel composed of fibrillar structures have a similar shape at different concentrations, although the intensity is larger for the gels with higher concentrations of 12-HSA. The SAXS analysis reveals that the cross-section of fibrils have square or circular shape (no anisotropic shape) with the radius of gyration 83 Å. On the other hand, for the turbid gel structural inhomnogeneity becomes significant with concentration. The gelation properties and the structures are found to be similar in the racemic HSA gel and the optically active (D-HSA) gel.

Aging of D-limonene-cleaned assemblies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Somer, T.A.

1994-04-01

The performance of 2000 electronic circuit variables was monitored throughout a 5000-hour exposure to + 160{degrees}F. the 2000 variables involve 36 electronic assemblies, cleaned with various solvents, including d-limonene, as a replacement for TCE. The assemblies were divided into four groups, including a TCE-cleaned control group at room temperature. Of the three groups exposed at + 160{degrees}F, one was cleaned in TCE, one was cleaned in d-limonene, and one was kept in a saturated d-limonene atmosphere. No performance degradation was observed with any of the groups, including the worst case exposure in a saturated d-limonene atmosphere.

Differently ordered TiO2 nanoarrays regulated by solvent polarity, and their photocatalytic performances

NASA Astrophysics Data System (ADS)

Hu, Wenyuan; Dong, Faqin; Zhang, Jing; Liu, Mingxue; He, Huichao; Wu, Yadong; Yang, Dingming; Deng, Hongquan

2018-06-01

Special TiO2 arrays with exposed facets were prepared in different solvents by low- temperature solvothermal synthesis. The morphology, phase and photocatalytic performance influenced by the various solvent polarities were characterized using field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectra and electrochemical testing. The results show that differences of solvent polarity are the main force driving differences in array growth; therefore, anatase TiO2 arrays with different crystal facets can be synthesized by tuning solvent polarity. TiO2 arrays prepared in cyclohexane are the best at oxidizing methyl orange through photocatalysis, followed by arrays prepared in toluene and ethanol. Arrays prepared in toluene are the best at reducing Cr(VI) photocatalytically, followed by those prepared in cyclohexane and ethanol. These differences in photocatalytic power are due to the ratio among the different crystal facets that are exposed, which affects the migration behavior of the photogenerated electrons and holes. In addition, the probable growth mechanisms of self-assembled ordered TiO2 arrays in different solvents are described.

Cyclic Solvent Vapor Annealing for Rapid, Robust Vertical Orientation of Features in BCP Thin Films

NASA Astrophysics Data System (ADS)

Paradiso, Sean; Delaney, Kris; Fredrickson, Glenn

2015-03-01

Methods for reliably controlling block copolymer self assembly have seen much attention over the past decade as new applications for nanostructured thin films emerge in the fields of nanopatterning and lithography. While solvent assisted annealing techniques are established as flexible and simple methods for achieving long range order, solvent annealing alone exhibits a very weak thermodynamic driving force for vertically orienting domains with respect to the free surface. To address the desire for oriented features, we have investigated a cyclic solvent vapor annealing (CSVA) approach that combines the mobility benefits of solvent annealing with selective stress experienced by structures oriented parallel to the free surface as the film is repeatedly swollen with solvent and dried. Using dynamical self-consistent field theory (DSCFT) calculations, we establish the conditions under which the method significantly outperforms both static and cyclic thermal annealing and implicate the orientation selection as a consequence of the swelling/deswelling process. Our results suggest that CSVA may prove to be a potent method for the rapid formation of highly ordered, vertically oriented features in block copolymer thin films.

Phase Behavior of a Single Structured Ionomer Chain in Solution

DOE PAGES

Aryal, Dipak; Etampawala, Thusitha; Perahia, Dvora; ...

2014-08-14

Structured polymers offer a means to tailor transport pathways within mechanically stable manifolds. Here we examine the building block of such a membrane, namely a single large pentablock co-polymer that consist of a center block of a randomly sulfonated polystyrene, designed for transport, tethered to poly-ethylene-r-propylene and end-capped by poly-t-butyl styrene, for mechanical stability,using molecular dynamics simulations. The polymer structure in a cyclohexane-heptane mixture, a technologically viable solvent, and in water, a poor solvent for all segments and a ubiquitous substance is extracted. In all solvents the pentablock collapsed into nearly spherical aggregates where the ionic block is segregated. Inmore » hydrophobic solvents, the ionic block resides in the center, surrounded by swollen intermix of flexible and end blocks. In water all blocks are collapsed with the sulfonated block residing on the surface. Our results demonstrate that solvents drive different local nano-segregation, providing a gateway to assemble membranes with controlled topology.« less

MICROWAVE-ACCELERATED MULTICOMPONENT REACTIONS UNDER SOLVENT-FREE CONDITIONS

EPA Science Inventory

The application of microwave-accelerated solventless synthetic protocols in multicomponent (MCC) reactions will be exemplified by several condensation and cyclization reactions including the rapid one-pot assembly of valuable heterocyclic compounds from in situ generated intermed...

Hierarchically arranged helical fibre actuators driven by solvents and vapours.

PubMed

Chen, Peining; Xu, Yifan; He, Sisi; Sun, Xuemei; Pan, Shaowu; Deng, Jue; Chen, Daoyong; Peng, Huisheng

2015-12-01

Mechanical responsiveness in many plants is produced by helical organizations of cellulose microfibrils. However, simple mimicry of these naturally occurring helical structures does not produce artificial materials with the desired tunable actuations. Here, we show that actuating fibres that respond to solvent and vapour stimuli can be created through the hierarchical and helical assembly of aligned carbon nanotubes. Primary fibres consisting of helical assemblies of multiwalled carbon nanotubes are twisted together to form the helical actuating fibres. The nanoscale gaps between the nanotubes and micrometre-scale gaps among the primary fibres contribute to the rapid response and large actuation stroke of the actuating fibres. The compact coils allow the actuating fibre to rotate reversibly. We show that these fibres, which are lightweight, flexible and strong, are suitable for a variety of applications such as energy-harvesting generators, deformable sensing springs and smart textiles.

Stability of anti-reflection coatings via the self-assembly encapsulation of silica nanoparticles by diazo-resins

NASA Astrophysics Data System (ADS)

Metzman, Jonathan S.; Ridley, Jason I.; Khalifa, Moataz B.; Heflin, James R.

2015-12-01

A modified silica nanoparticle (MSNP) solution was formed by the encapsulation of negatively charged silica nanoparticles by the UV-crosslinkable polycation oligomer diazo-resin (DAR). Appropriate DAR encapsulation concentrations were determined by use of zeta-potential and dynamic light scattering measurements. The MSNPs were used in conjunction with poly(styrene sulfonate) (PSS) to grow homogenous ionic self-assembled multilayer anti-reflection coatings. Stability was induced within the films by the exposure of UV-irradiation that allowed for crosslinking of the DAR and PSS. The films were characterized by UV/vis/IR spectroscopy and field emission scanning electron microscopy. The transmission and reflection levels were >98.5% and <0.05%, respectively. The refractive indices resided in the 1.25-1.26 range. The solvent stability was tested by sonication of the films in a ternary solvent (H2O/DMF/ZnCl2 3:5:2 w/w/w).

Hierarchically arranged helical fibre actuators driven by solvents and vapours

NASA Astrophysics Data System (ADS)

Chen, Peining; Xu, Yifan; He, Sisi; Sun, Xuemei; Pan, Shaowu; Deng, Jue; Chen, Daoyong; Peng, Huisheng

2015-12-01

Mechanical responsiveness in many plants is produced by helical organizations of cellulose microfibrils. However, simple mimicry of these naturally occurring helical structures does not produce artificial materials with the desired tunable actuations. Here, we show that actuating fibres that respond to solvent and vapour stimuli can be created through the hierarchical and helical assembly of aligned carbon nanotubes. Primary fibres consisting of helical assemblies of multiwalled carbon nanotubes are twisted together to form the helical actuating fibres. The nanoscale gaps between the nanotubes and micrometre-scale gaps among the primary fibres contribute to the rapid response and large actuation stroke of the actuating fibres. The compact coils allow the actuating fibre to rotate reversibly. We show that these fibres, which are lightweight, flexible and strong, are suitable for a variety of applications such as energy-harvesting generators, deformable sensing springs and smart textiles.

Solvent effect on the self-assembly of salt solvates of an antihypertensive drug azilsartan and 2-methylimidazole

NASA Astrophysics Data System (ADS)

Zhang, Xian-Rui; Zhang, Lei

2017-06-01

Three salt solvates of azilsartan (AZ) with 2-methylimidazole (2MI) (namely AZ-2MI-H2O, AZ-2MI-ACE and AZ-2MI-THF) and one azilsartan solvate (AZ-DIO, ACE = acetone, THF = tetrahydrofuran, and DIO = 1,4-dioxane) were manufactured by solvent-controlled self-assembly in aqueous-organic solutions. The experimental result of AZ-DIO shows that AZ is high affinity to DIO molecule, which has a unique ability to prevent salt formation between AZ and 2MI. Thermal studies of three salt solvates exhibit poor thermodynamic stability in environmental conditions. Solubility experiments show that AZ-2MI-ACE and AZ-2MI-THF are unstable and convert to AZ-2MI-H2O in aqueous solution, and that AZ-2MI-H2O exhibits increased solubility and retention stability in an aqueous medium compared with the commercial AZ-A crystalline form.

Effects of solvent evaporation conditions on solvent vapor annealed cylinder-forming block polymer thin films

NASA Astrophysics Data System (ADS)

Grant, Meagan; Jakubowski, William; Nelson, Gunnar; Drapes, Chloe; Baruth, A.

Solvent vapor annealing is a less time and energy intensive method compared to thermal annealing, to direct the self-assembly of block polymer thin films. Periodic nanostructures have applications in ultrafiltration, magnetic arrays, or other structures with nanometer dimensions, driving its continued interest. Our goal is to create thin films with hexagonally packed, perpendicular aligned cylinders of poly(lactide) in a poly(styrene) matrix that span the thickness of the film with low anneal times and low defect densities, all with high reproducibility, where the latter is paramount. Through the use of our computer-controlled, pneumatically-actuated, purpose-built solvent vapor annealing chamber, we have the ability to monitor and control vapor pressure, solvent concentration within the film, and solvent evaporation rate with unprecedented precision and reliability. Focusing on evaporation, we report on two previously unexplored areas, chamber pressure during solvent evaporation and the flow rate of purging gas aiding the evaporation. We will report our exhaustive results following atomic force microscopy analysis of films exposed to a wide range of pressures and flow rates. Reliably achieving well-ordered films, while occurring within a large section of this parameter space, was correlated with high-flow evaporation rates and low chamber pressures. These results have significant implications on other methods of solvent annealing, including ``jar'' techniques.

Polar-solvent-free colloidal synthesis of highly luminescent alkylammonium lead halide perovskite nanocrystals

NASA Astrophysics Data System (ADS)

Vybornyi, Oleh; Yakunin, Sergii; Kovalenko, Maksym V.

2016-03-01

A novel synthesis of hybrid organic-inorganic lead halide perovskite nanocrystals (CH3NH3PbX3, X = Br or I) that does not involve the use of dimethylformamide or other polar solvents is presented. The reaction between methylamine and PbX2 salts is conducted in a high-boiling nonpolar solvent (1-octadecene) in the presence of oleylamine and oleic acid as coordinating ligands. The resulting nanocrystals are characterized by high photoluminescence quantum efficiencies of 15-50%, outstanding phase purity and tunable shapes (nanocubes, nanowires, and nanoplatelets). Nanoplatelets spontaneously assemble into micrometer-length wires by face-to-face stacking. In addition, we demonstrate amplified spontaneous emission from thin films of green-emitting CH3NH3PbBr3 nanowires with low pumping thresholds of 3 μJ cm-2.A novel synthesis of hybrid organic-inorganic lead halide perovskite nanocrystals (CH3NH3PbX3, X = Br or I) that does not involve the use of dimethylformamide or other polar solvents is presented. The reaction between methylamine and PbX2 salts is conducted in a high-boiling nonpolar solvent (1-octadecene) in the presence of oleylamine and oleic acid as coordinating ligands. The resulting nanocrystals are characterized by high photoluminescence quantum efficiencies of 15-50%, outstanding phase purity and tunable shapes (nanocubes, nanowires, and nanoplatelets). Nanoplatelets spontaneously assemble into micrometer-length wires by face-to-face stacking. In addition, we demonstrate amplified spontaneous emission from thin films of green-emitting CH3NH3PbBr3 nanowires with low pumping thresholds of 3 μJ cm-2. Electronic supplementary information (ESI) available: Materials and methods, additional figures. See DOI: 10.1039/c5nr06890h

High-throughput 96-well solvent mediated sonic blending synthesis and on-plate solid/solution stability characterization of pharmaceutical cocrystals.

PubMed

Luu, Van; Jona, Janan; Stanton, Mary K; Peterson, Matthew L; Morrison, Henry G; Nagapudi, Karthik; Tan, Helming

2013-01-30

A 96-well high-throughput cocrystal screening workflow has been developed consisting of solvent-mediated sonic blending synthesis and on-plate solid/solution stability characterization by XRPD. A strategy of cocrystallization screening in selected blend solvents including water mixtures is proposed to not only manipulate solubility of the cocrystal components but also differentiate physical stability of the cocrystal products. Caffeine-oxalic acid and theophylline-oxalic acid cocrystals were prepared and evaluated in relation to saturation levels of the cocrystal components and stability of the cocrystal products in anhydrous and hydrous solvents. AMG 517 was screened with a number of coformers, and solid/solution stability of the resulting cocrystals on the 96-well plate was investigated. A stability trend was observed and confirmed that cocrystals comprised of lower aqueous solubility coformers tended to be more stable in water. Furthermore, cocrystals which could be isolated under hydrous solvent blending condition exhibited superior physical stability to those which could only be obtained under anhydrous condition. This integrated HTS workflow provides an efficient route in an API-sparing approach to screen and identify cocrystal candidates with proper solubility and solid/solution stability properties. Copyright © 2012 Elsevier B.V. All rights reserved.

Role of solvent-mediated carbodiimide cross-linking in fabrication of electrospun gelatin nanofibrous membranes as ophthalmic biomaterials.

PubMed

Chou, Shih-Feng; Luo, Li-Jyuan; Lai, Jui-Yang; Ma, David Hui-Kang

2017-02-01

Due to their ability to mimic the structure of extracellular matrix, electrospun gelatin nanofibers are promising cell scaffolding materials for tissue engineering applications. However, the hydrophilic gelatin molecules usually need stabilization before use in aqueous physiological environment. Considering that biomaterials cross-linked via film immersion technique may have a more homogeneous cross-linked structure than vapor phase cross-linking, this work aims to investigate the chemical modification of electrospun gelatin nanofibrous membranes by liquid phase carbodiimide in the presence of ethanol/water co-solvents with varying ethanol concentrations ranging from 80 to 99.5vol%. The results of characterization showed that increasing water content in the binary reaction solvent system increases the extent of cross-linking of gelatin nanofibers, but simultaneously promotes the effect of biopolymer swelling and distortion in fiber mat structure. As compared to non-cross-linked counterparts, carbodiimide treated gelatin nanofibrous mats exhibited better thermal and biological stability where the shrinkage temperature and resistance to enzymatic degradation varied in response to ethanol/water solvent composition-mediated generation of cross-links. Irrespective of their cross-linking density, all studied membrane samples did not induce any responses in ocular epithelial cell cultures derived from cornea, lens, and retina. Unlike many other cross-linking agents and/or methods (e.g., excessive vapor phase cross-linking) that may pose a risk of toxicity, our study demonstrated that these nanofibrous materials are well tolerated by anterior segment tissues. These findings also indicate the safety of using ethanol/water co-solvents for chemical cross-linking of gelatin to engineer nanofibrous materials with negligible biological effects. In summary, the present results suggest the importance of solvent-mediated carbodiimide cross-linking in modulating structure-property relationship without compromising in vitro and in vivo biocompatibility of electrospun gelatin nanofibers for future ophthalmic applications. Copyright © 2016 Elsevier B.V. All rights reserved.

Solvent-coordinate free-energy landscape view of water-mediated ion-pair dissociation

NASA Astrophysics Data System (ADS)

Yonetani, Yoshiteru

2017-12-01

Water-mediated ion-pair dissociation is studied by molecular dynamics simulations of NaCl in water. Multidimensional free-energy analysis clarifies the relation between two essential solvent coordinates: the water coordination number and water-bridge formation. These two are related in a complex way. Both are necessary to describe ion-pair dissociation. The mechanism constructed with both solvent variables clearly shows the individual roles. The water coordination number is critical for starting ion-pair dissociation. Water-bridge formation is also important because it increases the likelihood of ion-pair dissociation by reducing the dissociation free-energy barrier. Additional Ca-Cl and NH4-Cl calculations show that these conclusions are unaffected by changes in the ion charge and shape. The present results will contribute to future explorations of many other molecular events such as surface water exchange and protein-ligand dissociation because the same mechanism is involved in such events.

The influence of self-assembling supramolecular structures on the passive membrane transport of ion-paired molecules.

PubMed

Benaouda, F; Brown, M B; Shah, B; Martin, G P; Jones, S A

2012-12-15

Weak ion-ion interactions, such as those associated with ion-pair formation, are difficult to isolate and characterise in the liquid state, but they have the potential to alter significantly the physicochemical behaviour of molecules in solution. The aim of this work was to gain a better understanding of how ion-ion interactions influenced passive membrane transport. The test system was composed of propylene (PG) glycol, water and diclofenac diethylamine (DDEA). Infrared spectroscopy was employed to determine the nature of the DDEA ion-pair interactions and the drug-vehicle association. Passive transport was assessed using homogeneous synthetic membranes. Solution-state analysis demonstrated that the ion-pair was unperturbed by vehicle composition changes, but the solvent-DDEA interactions were modified. DDEA-PG/water hydrogen bonding influenced the ion-pair solubility (X(dev)) and the solvent interactions slowed transport rate in PG-rich vehicles (0.84±0.05 μg cm(-2) h(-1), at ln(X(dev))=0.57). In water-rich co-solvents, the presence of strong water structuring facilitated a significant increase (p<0.05) in transmembrane penetration rate (e.g. 4.33±0.92 μg cm(-2) h(-1), at ln(X(dev))=-0.13). The data demonstrates that weak ion-ion interactions can result in the embedding of polar entities within a stable solvent complex and spontaneous supramolecular assembly should be considered when interpreting transmembrane transport processes of ionic molecules. Copyright © 2012 Elsevier B.V. All rights reserved.

Binary breath figures for straightforward and controllable self-assembly of microspherical caps.

PubMed

Gong, Jianliang; Xu, Bingang; Tao, Xiaoming; Li, Lei

2016-05-11

The intense interest surrounding asymmetrical microparticles originates from their unique anisotropic properties and promising applications. In this work, direct self-assembly of polymeric microspherical caps without the assistance of any additives has been achieved by using low-surface-tension methanol (MeOH) and high-surface-tension water as binary breath figures (BFs). With the evaporation of polystyrene (PS) solution containing low-boiling-point solvent in the binary vapors, the formed MeOH BFs could quickly diffuse into solution, while water BFs tended to remain at the solution surface. This led to the formation of a gradient nonsolvent layer at the vapor/solution interface, which induced the formation of nuclei and guided further asymmetrical growth of polymer particles. After the spontaneous removal of MeOH, water and residual solvent by evaporation, polymeric microspherical caps were left on the substrate. Through controlling the proportion of water introduced by adjusting the ratios of MeOH and water, polymeric microspherical caps with a range of controllable shapes (divided at different positions of a sphere) were successfully obtained. The formation mechanism was explained based on the difference of vapor pressure, surface tension and miscibility between the employed solvents and nonsolvents. A solvent possessing a high vapor pressure, low surface tension and good miscibility with MeOH contributed to the formation of microspherical caps. This flexible, green and straightforward technique is a nondestructive strategy, and avoids complicated work on design, preparation and removal of hard templates and additives.

Supramolecular guests in solvent driven block copolymer assembly: From internally structured nanoparticles to micelles

PubMed Central

Klinger, Daniel; Robb, Maxwell J.; Spruell, Jason M.; Lynd, Nathaniel A.; Hawker, Craig J.

2014-01-01

Supramolecular interactions between different hydrogen-bonding guests and poly(2-vinyl pyridine)-block-poly (styrene) can be exploited to prepare remarkably diverse self-assembled nanostructures in dispersion from a single block copolymer (BCP). The characteristics of the BCP can be efficiently controlled by tailoring the properties of a guest which preferentially binds to the P2VP block. For example, the incorporation of a hydrophobic guest creates a hydrophobic BCP complex that forms phase separated nanoparticles upon self-assembly. Conversely, the incorporation of a hydrophilic guest results in an amphiphilic BCP complex that forms spherical micelles in water. The ability to tune the self-assembly behavior and access dramatically different nanostructures from a single BCP substrate demonstrates the exceptional versatility of the self-assembly of BCPs driven by supramolecular interactions. This approach represents a new methodology that will enable the further design of complex, responsive self-assembled nanostructures. PMID:25525473

Gold nanorod linking to control plasmonic properties in solution and polymer nanocomposites.

PubMed

Ferrier, Robert C; Lee, Hyun-Su; Hore, Michael J A; Caporizzo, Matthew; Eckmann, David M; Composto, Russell J

2014-02-25

A novel, solution-based method is presented to prepare bifunctional gold nanorods (B-NRs), assemble B-NRs end-to-end in various solvents, and disperse linked B-NRs in a polymer matrix. The B-NRs have poly(ethylene glycol) grafted along its long axis and cysteine adsorbed to its ends. By controlling cysteine coverage, bifunctional ligands or polymer can be end-grafted to the AuNRs. Here, two dithiol ligands (C6DT and C9DT) are used to link the B-NRs in organic solvents. With increasing incubation time, the nanorod chain length increases linearly as the longitudinal surface plasmon resonance shifts toward lower adsorption wavelengths (i.e., red shift). Analogous to step-growth polymerization, the polydispersity in chain length also increases. Upon adding poly(ethylene glycol) or poly(methyl methacrylate) to chloroform solution with linked B-NR, the nanorod chains are shown to retain end-to-end linking upon spin-casting into PEO or PMMA films. Using quartz crystal microbalance with dissipation (QCM-D), the mechanism of nanorod linking is investigated on planar gold surfaces. At submonolayer coverage of cysteine, C6DT molecules can insert between cysteines and reach an areal density of 3.4 molecules per nm(2). To mimic the linking of Au NRs, this planar surface is exposed to cysteine-coated Au nanoparticles, which graft at 7 NPs per μm(2). This solution-based method to prepare, assemble, and disperse Au nanorods is applicable to other nanorod systems (e.g., CdSe) and presents a new strategy to assemble anisotropic particles in organic solvents and polymer coatings.

New nanoparticles obtained by co-assembly of amphiphilic cyclodextrins and nonlamellar single-chain lipids: Preparation and characterization.

PubMed

Nguyễn, Cảnh Hưng; Putaux, Jean-Luc; Santoni, Gianluca; Tfaili, Sana; Fourmentin, Sophie; Coty, Jean-Baptiste; Choisnard, Luc; Gèze, Annabelle; Wouessidjewe, Denis; Barratt, Gillian; Lesieur, Sylviane; Legrand, François-Xavier

2017-10-15

This work aimed at preparing new nanoscale assemblies based on an amphiphilic bio-esterified β-cyclodextrin (β-CD), substituted at the secondary face with n-decanoic fatty acid chains (β-CD-C 10 ), and monoolein (MO) as new carriers for parenteral drug delivery. Stable binary (β-CD-C 10 /MO) and ternary (β-CD-C 10 /MO/stabilizer) nanoscale assemblies close to 100nm in size were successfully prepared in water by the solvent displacement method. The generated nanoparticles were fully characterized by dynamic light scattering, transmission electron microscopy, small-angle X-ray scattering, residual solvent analysis, complement activation and the contribution of each formulation parameter was determined by principal component analysis. The β-CD-C 10 units were shown to self-organize into nanoparticles with a hexagonal supramolecular packing that was significantly modulated by the molar ratio of the constituents and the presence of a steric or electrostatic stabilizer (DOPE-PEG 2000 or DOPA/POPA, respectively). Indeed, nanoparticles differing in morphology and in hexagonal lattice parameters were obtained while the co-existence of multiple mesophases was observed in some formulations, in particular for the β-CD-C 10 /MO/DOPA and β-CD-C 10 /MO/POPA systems. The mixed β-CD-C 10 /MO/DOPE-PEG 2000 nanoparticles (49:49:2 in mol%) appeared to be the most suitable for use as a drug delivery system since they contained a very low amount of residual solvent and showed a low level of complement C3 activation. Copyright © 2017 Elsevier B.V. All rights reserved.

Fluctuation-driven anisotropy in effective pair interactions between nanoparticles: Thiolated gold nanoparticles in ethane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jabes, B. Shadrack; Yadav, Hari O. S.; Chakravarty, Charusita, E-mail: charus@chemistry.iitd.ac.in

2014-10-21

Fluctuations within the ligand shell of a nanoparticle give rise to a significant degree of anisotropy in effective pair interactions for low grafting densities [B. Bozorgui, D. Meng, S. K. Kumar, C. Chakravarty, and A. Cacciuto, Nano Lett. 13, 2732 (2013)]. Here, we examine the corresponding fluctuation-driven anisotropy for gold nanocrystals densely passivated with short ligands. In particular, we consider gold nanocrystals capped by alkylthiols, both in vacuum and in ethane solvent at high density. As in the preceding study, we show that the anisotropy in the nanoparticle pair potential can be quantified by an angle-dependent correction term to themore » isotropic potential of mean force (PMF). We find that the anisotropy of the ligand shells is distance dependent, and strongly influenced by ligand interdigitation effects as well as expulsion of ligand chains from the interparticle region at short distances. Such fluctuation-driven anisotropy can be significant for alkylthiol-coated gold nanoparticles, specially for longer chain lengths, under good solvent conditions. The consequences of such anisotropy for self-assembly, specially as a function of grafting density, solvent quality and at interfaces, should provide some interesting insights in future work. Our results clearly show that an isotropic two-body PMF cannot adequately describe the thermodynamics and assembly behavior of nanoparticles in this dense grafting regime and inclusion of anisotropic effects, as well as possibly many-body interactions, is necessary. Extensions of this approach to other passivated nanoparticle systems and implications for self-assembly are considered.« less

Gold Nanorod Linking to Control Plasmonic Properties in Solution and Polymer Nanocomposites

PubMed Central

2015-01-01

A novel, solution-based method is presented to prepare bifunctional gold nanorods (B-NRs), assemble B-NRs end-to-end in various solvents, and disperse linked B-NRs in a polymer matrix. The B-NRs have poly(ethylene glycol) grafted along its long axis and cysteine adsorbed to its ends. By controlling cysteine coverage, bifunctional ligands or polymer can be end-grafted to the AuNRs. Here, two dithiol ligands (C6DT and C9DT) are used to link the B-NRs in organic solvents. With increasing incubation time, the nanorod chain length increases linearly as the longitudinal surface plasmon resonance shifts toward lower adsorption wavelengths (i.e., red shift). Analogous to step-growth polymerization, the polydispersity in chain length also increases. Upon adding poly(ethylene glycol) or poly(methyl methacrylate) to chloroform solution with linked B-NR, the nanorod chains are shown to retain end-to-end linking upon spin-casting into PEO or PMMA films. Using quartz crystal microbalance with dissipation (QCM-D), the mechanism of nanorod linking is investigated on planar gold surfaces. At submonolayer coverage of cysteine, C6DT molecules can insert between cysteines and reach an areal density of 3.4 molecules per nm2. To mimic the linking of Au NRs, this planar surface is exposed to cysteine-coated Au nanoparticles, which graft at 7 NPs per μm2. This solution-based method to prepare, assemble, and disperse Au nanorods is applicable to other nanorod systems (e.g., CdSe) and presents a new strategy to assemble anisotropic particles in organic solvents and polymer coatings. PMID:24483622

Gold-nanoparticle-mediated jigsaw-puzzle-like assembly of supersized plasmonic DNA origami.

PubMed

Yao, Guangbao; Li, Jiang; Chao, Jie; Pei, Hao; Liu, Huajie; Zhao, Yun; Shi, Jiye; Huang, Qing; Wang, Lianhui; Huang, Wei; Fan, Chunhai

2015-03-02

DNA origami has rapidly emerged as a powerful and programmable method to construct functional nanostructures. However, the size limitation of approximately 100 nm in classic DNA origami hampers its plasmonic applications. Herein, we report a jigsaw-puzzle-like assembly strategy mediated by gold nanoparticles (AuNPs) to break the size limitation of DNA origami. We demonstrated that oligonucleotide-functionalized AuNPs function as universal joint units for the one-pot assembly of parent DNA origami of triangular shape to form sub-microscale super-origami nanostructures. AuNPs anchored at predefined positions of the super-origami exhibited strong interparticle plasmonic coupling. This AuNP-mediated strategy offers new opportunities to drive macroscopic self-assembly and to fabricate well-defined nanophotonic materials and devices. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Columnar to nematic mesophase transition in mixtures of rhodium or copper soaps with hydrocarbon solvents

NASA Astrophysics Data System (ADS)

Ibn-Elhaj, M.; Guillon, D.; Skoulios, A.; Giroud-Godquin, A. M.; Marchon, J.-C.

1992-12-01

This paper describes observations of the mesomorphic behaviour of mixtures of rhodium eicosanoate or copper dodecanoate with solvents such as toluene, decahydronaphthalene, and (+) camphene. The mesophase found with these compounds at high temperatures turns from columnar to nematic when the weight fraction of the solvent (toluene, decahydronaphthalene is increased beyond a value of about 50%. The binary phase diagram of the copper compound with toluene was experimentally determined using polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. The novel feature of the nematic phase is that the basic physical object which align parallel to the nematic director are not individual molecules, but columns of molecules (one-dimensional supramolecular assemblies) which have lost the long-range lateral positional order characteristic of the columnar mesophase. These observations are discussed on the grounds of recent theoretical calculations. Cholesteric-like textures are observed for mixtures of rhodium eicosanoate with the chiral solvent (+) camphene.

Self-assembly of an imidazolate-bridged Fe(III)/Cu(II) heterometallic cage.

PubMed

Reichel, Florian; Clegg, Jack K; Gloe, Karsten; Gloe, Kerstin; Weigand, Jan J; Reynolds, Jason K; Li, Chun-Guang; Aldrich-Wright, Janice R; Kepert, Cameron J; Lindoy, Leonard F; Yao, Hong-Chang; Li, Feng

2014-01-21

A rare, discrete, mixed-valent, heterometallic Fe(III)/Cu(II) cage, [Cu6Fe8L8](ClO4)12·χsolvent (H3L = tris{[2-{(imidazole-4-yl)methylidene}amino]ethyl}amine), was designed and synthesized via metal-ion-directed self-assembly with neutral tripodal metalloligands. The formation of this coordination cage was demonstrated by X-ray crystallography, ESI mass spectrometry, FT-IR, and UV-vis-NIR spectroscopy.

Charge transport in fibre-based perylene-diimide transistors: effect of the alkyl substitution and processing technique.

PubMed

Savage, Rebecca C; Orgiu, Emanuele; Mativetsky, Jeffrey M; Pisula, Wojciech; Schnitzler, Tobias; Eversloh, Christian Lütke; Li, Chen; Müllen, Klaus; Samorì, Paolo

2012-04-07

We report a comparative study on the self-assembly from solution and electrical characterization of n-type semiconducting fibres obtained from five different perylenebis(dicarboximide) (PDI) derivatives. In particular we investigated the role of the nature of the alkyl chain covalently linked to the N,N' sites of the PDI in modulating the molecular solubility and aggregation capacity. We explored the morphologies of the self-assembled architectures physisorbed on dielectric surfaces and in particular how they can be modified by tuning the deposition and post-deposition procedures, i.e. by modulating the kinetics of the self-assembly process. To this end, alongside the conventional spin-coating, solvent vapour annealing (SVA) and solvent induced precipitation (SIP) have been employed. Both approaches led to fibres having widths of several hundred nanometres and lengths up to tens of micrometres. SVA formed isolated fibres which were tens of nanometres high, flat, and tapered at the ends. Conversely, SIP fibres exhibited nearly matching heights and widths, but organized into bundles. Despite these morphological differences, the same intermolecular packing is found by XRD in each type of structure, albeit with differing degrees of long-range order. The study of the electrical characteristics of the obtained low dimensional nano-assemblies has been accomplished by fabricating and characterizing organic field-effect transistors. This journal is © The Royal Society of Chemistry 2012

Kinase Mediated Regulation of 40S Ribosome Assembly in Human Breast Cancer

DTIC Science & Technology

2017-02-01

Ribosome assembly • Autophagy • CRISPR /Cas9 6 ACCOMPLISHMENTS Major goals The major goals in this reporting period were to use the CRISPR ...defects on ribosome assembly, drug sensitivity etc. Accomplishments under these goals To set up the CRISPR /Cas9 experiment, the Karbstein...recombinant Cas9, and then assayed CRISPR /Cas9 mediated cleavage of a PCR-generated DNA. This demonstrated that the guide RNAs we had designed based on

Spiral Countercurrent Chromatography

PubMed Central

Ito, Yoichiro; Knight, Martha; Finn, Thomas M.

2013-01-01

For many years, high-speed countercurrent chromatography conducted in open tubing coils has been widely used for the separation of natural and synthetic compounds. In this method, the retention of the stationary phase is solely provided by the Archimedean screw effect by rotating the coiled column in the centrifugal force field. However, the system fails to retain enough of the stationary phase for polar solvent systems such as the aqueous–aqueous polymer phase systems. To address this problem, the geometry of the coiled channel was modified to a spiral configuration so that the system could utilize the radially acting centrifugal force. This successfully improved the retention of the stationary phase. Two different types of spiral columns were fabricated: the spiral disk assembly, made by stacking multiple plastic disks with single or four interwoven spiral channels connected in series, and the spiral tube assembly, made by inserting the tetrafluoroethylene tubing into a spiral frame (spiral tube support). The capabilities of these column assemblies were successfully demonstrated by separations of peptides and proteins with polar two-phase solvent systems whose stationary phases had not been well retained in the earlier multilayer coil separation column for high-speed countercurrent chromatography. PMID:23833207

Peptide interfaces with graphene: an emerging intersection of analytical chemistry, theory, and materials.

PubMed

Russell, Shane R; Claridge, Shelley A

2016-04-01

Because noncovalent interface functionalization is frequently required in graphene-based devices, biomolecular self-assembly has begun to emerge as a route for controlling substrate electronic structure or binding specificity for soluble analytes. The remarkable diversity of structures that arise in biological self-assembly hints at the possibility of equally diverse and well-controlled surface chemistry at graphene interfaces. However, predicting and analyzing adsorbed monolayer structures at such interfaces raises substantial experimental and theoretical challenges. In contrast with the relatively well-developed monolayer chemistry and characterization methods applied at coinage metal surfaces, monolayers on graphene are both less robust and more structurally complex, levying more stringent requirements on characterization techniques. Theory presents opportunities to understand early binding events that lay the groundwork for full monolayer structure. However, predicting interactions between complex biomolecules, solvent, and substrate is necessitating a suite of new force fields and algorithms to assess likely binding configurations, solvent effects, and modulations to substrate electronic properties. This article briefly discusses emerging analytical and theoretical methods used to develop a rigorous chemical understanding of the self-assembly of peptide-graphene interfaces and prospects for future advances in the field.

The Effect of Small Molecule Additives on the Self-Assembly and Functionality of Protein-Polymer Diblock Copolymers

NASA Astrophysics Data System (ADS)

Thomas, Carla; Xu, Liza; Olsen, Bradley

2013-03-01

Self-assembly of globular protein-polymer block copolymers into well-defined nanostructures provides a route towards the manufacture of protein-based materials which maintains protein fold and function. The model material mCherry-b-poly(N-isopropyl acrylamide) forms self-assembled nanostructures from aqueous solutions via solvent evaporation. To improve retention of protein functionality when dehydrated, small molecules such as trehalose and glycerol are added in solution prior to solvent removal. With as little as 10 wt% additive, improvements in retained functionality of 20-60% are observed in the solid-state as compared to samples in which no additive is present. Higher additive levels (up to 50%) continue to show improvement until approximately 100% of the protein function is retained. These large gains are hypothesized to originate from the ability of the additives to replace hydrogen bonds normally fulfilled by water. The addition of trehalose in the bulk material also improves the thermal stability of the protein by 15-20 °C, while glycerol decreases the thermal stability. Materials containing up to 50% additives remain microphase separated, and, upon incorporation of additives, nanostructure domain spacing tends to increase, accompanied by order-order transitions.

Theoretical insights into aggregation-induced helicity modulation of a perylene bisimide derivative.

PubMed

Liang, Lijun; Li, Xin

2018-02-12

Formation of helical chiroptical self-assemblies via noncovalent interaction is a widely observed phenomenon in nature, the mechanism of which remains insufficiently understood. Employing an amphiphilic perylene-sugar dyad molecule (PBI-HAG) as an example, we report that the modulatable supramolecular helicity may emerge from an aggregating process that is dominated by competition between two types of noncovalent interaction: hydrogen bonding and π-π stacking. The interplay between these two driving forces, which is greatly affected by the solvent environment, determines the morphology the supramolecular assembly of PBI-HAGs. In particular, a non-layered supramolecular structure was formed in octane owing to stabilization effects of intermolecular hydrogen bonds, whereas a layered supramolecular structure was formed in water because of energetically favorable π-π stacking of aromatic rings. The formation of distinct supramolecular architectures in different solvents was reinforced by simulated circular dichroism spectra, which show opposite signals consistent with experimental observations. The results of this study could help us understand aggregation-induced supramolecular chirality of noncovalent self-assemblies. Graphical abstract Left Typical structures of amphiphilic perylene-sugar dyad (PBI-HAG) aggregates in different octane and water. Right Simulated CD and UV-Vis spectra of core PBIs aggregates in octane and water.

Plasticity of an Amorphous Assembly of Elastic Gel Beads

NASA Astrophysics Data System (ADS)

Grosshans, D.; Knaebel, A.; Lequeux, F.

1995-01-01

We have studied the rheological properties of an assembly of swollen gel beads in a lack of solvent. The system is an amorphous assembly of packed soft spheres in a given volume. We have studied the plastic behavior of the system, and interpreted it in terms of bead rearrangements within the assembly. Nous avons étudié les propriétés rhéologiques d'un assemblage de billes de gel gonflées en défaut de solvant. Le système est donc une assemblée amorphe de sphères molles écrasées à volume total constant. Nous avons étudié divers aspects du comportement plastique et nous l'avons interprété en termes de réorganisations de billes dans l'assemblage.

Formalism for calculation of polymer-solvent-mediated potential

NASA Astrophysics Data System (ADS)

Zhou, Shiqi

2006-07-01

A simple theoretical approach is proposed for calculation of a solvent-mediated potential (SMP) between two colloid particles immersed in a polymer solvent bath in which the polymer is modeled as a chain with intramolecular degrees of freedom. The present recipe is only concerned with the estimation of the density profile of a polymer site around a single solute colloid particle instead of two solute colloid particles separated by a varying distance as done in existing calculational methods for polymer-SMP. Therefore the present recipe is far simpler for numerical implementation than the existing methods. The resultant predictions for the polymer-SMP and polymer solvent-mediated mean force (polymer-SMMF) are in very good agreement with available simulation data. With the present recipe, change tendencies of the contact value and second virial coefficiency of the SMP as a function of size ratio between the colloid particle and polymer site, the number of sites per chain, and the polymer concentration are investigated in detail. The metastable critical polymer concentration as a function of size ratio and the number of sites per chain is also reported for the first time. To yield the numerical solution of the present recipe at less than 1min on a personal computer, a rapid and accurate algorithm for the numerical solution of the classical density functional theory is proposed to supply rapid and accurate estimation of the density profile of the polymer site as an input into the present formalism.

First-Principles Molecular Dynamics Studies of Organometallic Complexes and Homogeneous Catalytic Processes.

PubMed

Vidossich, Pietro; Lledós, Agustí; Ujaque, Gregori

2016-06-21

Computational chemistry is a valuable aid to complement experimental studies of organometallic systems and their reactivity. It allows probing mechanistic hypotheses and investigating molecular structures, shedding light on the behavior and properties of molecular assemblies at the atomic scale. When approaching a chemical problem, the computational chemist has to decide on the theoretical approach needed to describe electron/nuclear interactions and the composition of the model used to approximate the actual system. Both factors determine the reliability of the modeling study. The community dedicated much effort to developing and improving the performance and accuracy of theoretical approaches for electronic structure calculations, on which the description of (inter)atomic interactions rely. Here, the importance of the model system used in computational studies is highlighted through examples from our recent research focused on organometallic systems and homogeneous catalytic processes. We show how the inclusion of explicit solvent allows the characterization of molecular events that would otherwise not be accessible in reduced model systems (clusters). These include the stabilization of nascent charged fragments via microscopic solvation (notably, hydrogen bonding), transfer of charge (protons) between distant fragments mediated by solvent molecules, and solvent coordination to unsaturated metal centers. Furthermore, when weak interactions are involved, we show how conformational and solvation properties of organometallic complexes are also affected by the explicit inclusion of solvent molecules. Such extended model systems may be treated under periodic boundary conditions, thus removing the cluster/continuum (or vacuum) boundary, and require a statistical mechanics simulation technique to sample the accessible configurational space. First-principles molecular dynamics, in which atomic forces are computed from electronic structure calculations (namely, density functional theory), is certainly the technique of choice to investigate chemical events in solution. This methodology is well established and thanks to advances in both algorithms and computational resources simulation times required for the modeling of chemical events are nowadays accessible, though the computational requirements use to be high. Specific applications reviewed here include mechanistic studies of the Shilov and Wacker processes, speciation in Pd chemistry, hydrogen bonding to metal centers, and the dynamics of agostic interactions.

Aging of d-Limonene-cleaned assemblies. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Somer, T.A.

1995-08-01

The performance of 1600 electronic circuit variables was monitored throughout an 8000-hour exposure to +160{degrees}F. The variables involve 36 electronic assemblies, cleaned with various solvents, including d-Limonene, as a replacement for trichloroethylene (TCE). The assemblies were divided into four groups, including a TCE-cleaned control group at room temperature. Of the three groups exposed at +160{degrees}F, one was cleaned in TCE, one was cleaned in d-Limonene, and one was kept in a saturated d-Limonene atmosphere. No performance degradation was observed with any of the groups, including the worst-case exposure in a saturated d-Limonene atmosphere.

Assembly of synthetic cellulose I.

PubMed

Lee, J H; Brown, R M; Kuga, S; Shoda, S; Kobayashi, S

1994-08-02

Cellulose microfibrils with an electron diffraction pattern characteristic of crystalline native cellulose I have been assembled abiotically by means of a cellulase-catalyzed polymerization of beta-cellobiosyl fluoride substrate monomer in acetonitrile/acetate buffer. Substantial purification of the Trichoderma viride cellulase enzyme was found to be essential for the formation of the synthetic cellulose I allomorph. Assembly of synthetic cellulose I appears to be a result of a micellar aggregation of the partially purified enzyme and the substrate in an organic/aqueous solvent system favoring the alignment of glucan chains with the same polarity and extended chain conformation, resulting in crystallization to form the metastable cellulose I allomorph.

Trace Water as Prominent Factor to Induce Peptide Self-Assembly: Dynamic Evolution and Governing Interactions in Ionic Liquids.

PubMed

Wang, Juan; Yuan, Chengqian; Han, Yuchun; Wang, Yilin; Liu, Xiaomin; Zhang, Suojiang; Yan, Xuehai

2017-11-01

The interaction between water and biomolecules including peptides is of critical importance for forming high-level architectures and triggering life's functions. However, the bulk aqueous environment has limitations in detecting the kinetics and mechanisms of peptide self-assembly, especially relating to interactions of trace water. With ionic liquids (ILs) as a nonconventional medium, herein, it is discovered that trace amounts of water play a decisive role in triggering self-assembly of a biologically derived dipeptide. ILs provide a suitable nonaqueous environment, enabling us to mediate water content and follow the dynamic evolution of peptide self-assembly. The trace water is found to be involved in the assembly process of dipeptide, especially leading to the formation of stable noncovalent dipeptide oligomers in the early stage of nucleation, as evident by both experimental studies and theoretical simulations. The thermodynamics of the growth process is mainly governed by a synergistic effect of hydrophobic interaction and hydrogen bonds. Each step of assembly presents a different trend in thermodynamic energy. The dynamic evolution of assembly process can be efficiently mediated by changing trace water content. The decisive role of trace water in triggering and mediating self-assembly of biomolecules provides a new perspective in understanding supramolecular chemistry and molecular self-organization in biology. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Examination of the solution behaviors of the giant inorganic-organic amphiphilic hybrids

NASA Astrophysics Data System (ADS)

Zhang, Baofang

Presently, the self-assembly behaviors of traditional small surfactants and amphiphilic block copolymers are fairly well understood. In comparison, rather little is known about the self-assembly behaviors of the giant inorganic-organic amphiphilic hybrids in solution. It remains a wide open field to explore. Giant inorganic-organic amphiphilic hybrids, consisting of nanoscale inorganic clusters and organic functional groups, represent a novel class of functional hybrid materials. They have unique physical and chemical properties and potential applications in catalysis, electronic, optics, magnetic materials, medicine and biology. Therefore, as emerging building blocks, they have promising prospects in the advanced materials. In this PhD work, several representative giant inorganic-organic amphiphilic hybrids (triangular-shaped polyoxometalate (POM)-containing inorganic/organic amphiphilic hybrids, POM-containing fluorosurfactants hybrids, POM-containing peptide hybrids POM-peptide hybrids and polyhedral oligometric silsesquioxane (POSS)-polystyrene (PS) are chosen for studying their self-assembly behaviors in solution. Based on the knowledge of the physical chemistry, colloid and polymer science, we focus on the mechanism of the self-assembly process, and the morphology control of the supramolecular structures through the internal and external conditions, such as the composition of the giant amphiphilies, molecular architectures, solvent nature, temperature, concentration, and extrally added salts. It is found that the counterion-meditated interactions dominate the self-assembly of triangular-shaped hybrids in acetone/water mixed solutions, due to the highly dominant hydrophilic portions; the solvent-swelling effect, instead of the charge effect, dominates the whole self-assembly process of the POM-containing fluorosurfactants; the analogy between small surfactants and giant amphiphiles POSS-PS allows a rough assessment of the possible morphologies of the supramolecular structures, and the particular values of the molecular packing parameter can be translated via simple geometrical relations into specific shape of the equilibrium supramolecular structures. For the experiments, laser light scattering (LLS) technique is used to monitor the entire self-assembly processes. The morphology and size of the supramolecular structures are determined by using dynamic light scattering (DLS) and static light scattering (SLS). Electron microscopies (TEM, SEM and AFM) are used to confirm the assembly structures and size. The stability of the assembly solution system is characterized by zeta potential.

Strongly Iridescent Hybrid Photonic Sensors Based on Self-Assembled Nanoparticles for Hazardous Solvent Detection.

PubMed

Sato, Ayaka; Ikeda, Yuya; Yamaguchi, Koichi; Vohra, Varun

2018-03-16

Facile detection and the identification of hazardous organic solvents are essential for ensuring global safety and avoiding harm to the environment caused by industrial wastes. Here, we present a simple method for the fabrication of silver-coated monodisperse polystyrene nanoparticle photonic structures that are embedded into a polydimethylsiloxane (PDMS) matrix. These hybrid materials exhibit a strong green iridescence with a reflectance peak at 550 nm that originates from the close-packed arrangement of the nanoparticles. This reflectance peak measured under Wulff-Bragg conditions displays a 20 to 50 nm red shift when the photonic sensors are exposed to five commonly employed and highly hazardous organic solvents. These red-shifts correlate well with PDMS swelling ratios using the various solvents, which suggests that the observable color variations result from an increase in the photonic crystal lattice parameter with a similar mechanism to the color modulation of the chameleon skin. Dynamic reflectance measurements enable the possibility of clearly identifying each of the tested solvents. Furthermore, as small amounts of hazardous solvents such as tetrahydrofuran can be detected even when mixed with water, the nanostructured solvent sensors we introduce here could have a major impact on global safety measures as innovative photonic technology for easily visualizing and identifying the presence of contaminants in water.

Simulating Self-Assembly with Simple Models

NASA Astrophysics Data System (ADS)

Rapaport, D. C.

Results from recent molecular dynamics simulations of virus capsid self-assembly are described. The model is based on rigid trapezoidal particles designed to form polyhedral shells of size 60, together with an atomistic solvent. The underlying bonding process is fully reversible. More extensive computations are required than in previous work on icosahedral shells built from triangular particles, but the outcome is a high yield of closed shells. Intermediate clusters have a variety of forms, and bond counts provide a useful classification scheme

Non-aqueous cleaning solvent substitution

NASA Technical Reports Server (NTRS)

Meier, Gerald J.

1994-01-01

A variety of environmental, safety, and health concerns exist over use of chlorinated and fluorinated cleaning solvents. Sandia National Laboratories, Lawrence Livermore National Laboratories, and the Kansas City Division of AlliedSignal have combined efforts to focus on finding alternative cleaning solvents and processes which are effective, environmentally safe, and compliant with local, state, and federal regulations. An alternative solvent has been identified, qualified, and implemented into production of complex electronic assemblies, where aqueous and semi-aqueous cleaning processes are not allowed. Extensive compatibility studies were performed with components, piece-parts, and materials. Electrical testing and accelerated aging were used to screen for detrimental, long-term effects. A terpene, d-limonene, was selected as the solvent of choice, and it was found to be compatible with the components and materials tested. A brief history of the overall project will be presented, along with representative cleaning efficiency results, compatibility results, and residual solvent data. The electronics industry is constantly searching for proven methods and environmentally-safe materials to use in manufacturing processes. The information in this presentation will provide another option to consider on future projects for applications requiring high levels of quality, reliability, and cleanliness from non-aqueous cleaning processes.

Controlled assembly of nanoparticle structures: spherical and toroidal superlattices and nanoparticle-coated polymeric beads.

PubMed

Isojima, Tatsushi; Suh, Su Kyung; Vander Sande, John B; Hatton, T Alan

2009-07-21

The emulsion droplet solvent evaporation method has been used to prepare nanoclusters of monodisperse magnetite nanoparticles of varying morphologies depending on the temperature and rate of solvent evaporation and on the composition (solvent, presence of polymer, nanoparticle concentration, etc.) of the emulsion droplets. In the absence of a polymer, and with increasing solvent evaporation temperatures, the nanoparticles formed single- or multidomain crystalline superlattices, amorphous spherical aggregates, or toroidal clusters, as determined by the energetics and dynamics of the solvent evaporation process. When polymers that are incompatible with the nanoparticle coatings were included in the emulsion formulation, monolayer- and multilayer-coated polymer beads and partially coated Janus beads were prepared; the nanoparticles were expelled by the polymer as its concentration increased on evaporation of the solvent and accumulated on the surfaces of the beads in a well-ordered structure. The precise number of nanoparticle layers depended on the polymer/magnetic nanoparticle ratio in the oil droplet phase parent emulsion. The magnetic nanoparticle superstructures responded to the application of a modest magnetic field by forming regular chains with alignment of nonuniform structures (e.g., toroids and Janus beads) that are in accord with theoretical predictions and with observations in other systems.

Conformation of ionizable poly Para phenylene ethynylene in dilute solutions

DOE PAGES

Wijesinghe, Sidath; Maskey, Sabina; Perahia, Dvora; ...

2015-11-03

The conformation of dinonyl poly para phenylene ethynylenes (PPEs) with carboxylate side chains, equilibrated in solvents of different quality is studied using molecular dynamics simulations. PPEs are of interest because of their tunable electro-optical properties, chemical diversity, and functionality which are essential in wide range of applications. The polymer conformation determines the conjugation length and their assembly mode and affects electro-optical properties which are critical in their current and potential uses. The current study investigates the effect of carboxylate fraction on PPEs side chains on the conformation of chains in the dilute limit, in solvents of different quality. The dinonylmore » PPE chains are modeled atomistically, where the solvents are modeled both implicitly and explicitly. Dinonyl PPEs maintained a stretched out conformation up to a carboxylate fraction f of 0.7 in all solvents studied. The nonyl side chains are extended and oriented away from the PPE backbone in toluene and in implicit good solvent whereas in water and implicit poor solvent, the nonyl side chains are collapsed towards the PPE backbone. Thus, rotation around the aromatic ring is fast and no long range correlations are seen within the backbone.« less

Conformation of ionizable poly Para phenylene ethynylene in dilute solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wijesinghe, Sidath; Maskey, Sabina; Perahia, Dvora

The conformation of dinonyl poly para phenylene ethynylenes (PPEs) with carboxylate side chains, equilibrated in solvents of different quality is studied using molecular dynamics simulations. PPEs are of interest because of their tunable electro-optical properties, chemical diversity, and functionality which are essential in wide range of applications. The polymer conformation determines the conjugation length and their assembly mode and affects electro-optical properties which are critical in their current and potential uses. The current study investigates the effect of carboxylate fraction on PPEs side chains on the conformation of chains in the dilute limit, in solvents of different quality. The dinonylmore » PPE chains are modeled atomistically, where the solvents are modeled both implicitly and explicitly. Dinonyl PPEs maintained a stretched out conformation up to a carboxylate fraction f of 0.7 in all solvents studied. The nonyl side chains are extended and oriented away from the PPE backbone in toluene and in implicit good solvent whereas in water and implicit poor solvent, the nonyl side chains are collapsed towards the PPE backbone. Thus, rotation around the aromatic ring is fast and no long range correlations are seen within the backbone.« less

3D assembly of upconverting NaYF4 nanocrystals by AFM nanoxerography: creation of anti-counterfeiting microtags

NASA Astrophysics Data System (ADS)

Sangeetha, Neralagatta M.; Moutet, Pierre; Lagarde, Delphine; Sallen, Gregory; Urbaszek, Bernhard; Marie, Xavier; Viau, Guillaume; Ressier, Laurence

2013-09-01

Formation of 3D close-packed assemblies of upconverting NaYF4 colloidal nanocrystals (NCs) on surfaces, by Atomic Force Microscopy (AFM) nanoxerography is presented. The surface potential of the charge patterns, the NC concentration, the polarizability of the NCs and the polarity of the dispersing solvent are identified as the key parameters controlling the assembly of NaYF4 NCs into micropatterns of the desired 3D architecture. This insight allowed us to fabricate micrometer sized Quick Response (QR) codes encoded in terms of upconversion luminescence intensity or color. Topographically hidden messages could also be readily incorporated within these microtags. This work demonstrates that AFM nanoxerography has enormous potential for generating high-security anti-counterfeiting microtags.Formation of 3D close-packed assemblies of upconverting NaYF4 colloidal nanocrystals (NCs) on surfaces, by Atomic Force Microscopy (AFM) nanoxerography is presented. The surface potential of the charge patterns, the NC concentration, the polarizability of the NCs and the polarity of the dispersing solvent are identified as the key parameters controlling the assembly of NaYF4 NCs into micropatterns of the desired 3D architecture. This insight allowed us to fabricate micrometer sized Quick Response (QR) codes encoded in terms of upconversion luminescence intensity or color. Topographically hidden messages could also be readily incorporated within these microtags. This work demonstrates that AFM nanoxerography has enormous potential for generating high-security anti-counterfeiting microtags. Electronic supplementary information (ESI) available: Detailed experimental procedures for the synthesis of upconverting NaYF4 nanocrystals and their transmission electron microscopy images. KFM and AFM images corresponding to the assembly of positively charged β-NaYF4:Er3+,Yb3+ nanocrystals from water suspensions by AFM nanoxerography. Photoluminescence spectra of β-NaYF4:Er3+,Yb3+ nanocrystals in a hexane suspension and assembled on charge patterns. See DOI: 10.1039/c3nr02734a

Novel theranostic zinc phthalocyanine-phospholipid complex self-assembled nanoparticles for imaging-guided targeted photodynamic treatment with controllable ROS production and shape-assisted enhanced cellular uptake.

PubMed

Ma, Jinyuan; Li, Yang; Liu, Guihua; Li, Ai; Chen, Yilin; Zhou, Xinyi; Chen, Dengyue; Hou, Zhenqing; Zhu, Xuan

2018-02-01

The novel drug delivery system based on self-assembly of zinc phthalocyanine-soybean phosphatidylcholine (ZnPc-SPC) complex was developed by a co-solvent method followed by a nanoprecipitaion technique. DSPE-PEG-methotrexate (DSPE-PEG-MTX) was introduced on the surface of ZnPc-SPC self-assembled nanoparticles (ZS) to endow them with folate receptor-targeting property. NMR, XRD, FTIR, and UV-vis-NIR analysis demonstrated the weak molecular interaction between ZnPc and SPC. The ZS functionalized with DSPE-PEG-MTX (ZSPM) was successfully constructed with an average particle size of ∼170nm, a narrow size distribution, and could remain physiologically stable for at least 7days. In vitro cellular uptake and cytotoxicity studies demonstrated that ZSPM exhibited stronger cellular uptake efficacy and photodynamic cytotoxicity against HeLa and MCF-7 cells than ZS functionalized with DSPE-mPEG (ZSP) and free ZnPc. More importantly, ZSPM showed the enhanced accumulation effect at the tumor region compared with ZSP by the active-plus-passive targeting via enhanced permeability and retention (EPR) effect and folate receptor-mediated endocytosis. Furthermore, in vivo antitumor effect and histological analysis demonstrated the superior tumor growth inhibition effect of ZSPM. In addition, the needle-shape ZSP (ZSPN) exhibited better in vitro cellular uptake and in vivo tumor accumulation compared with ZSP due to the shape-assisted effect. Moreover, the interesting off-on switch effect of reactive oxygen species (ROS) production of ZnPc-SPC complex-based nanoparticles was discovered to achieve photodynamic treatment in a controllable way. These findings suggested that the ZnPc-SPC complex-based self-assembled nanoparticles could serve as a promising and effective formulation to achieve tumor-targeting fluorescence imaging and enhanced photodynamic treatment. Copyright © 2017. Published by Elsevier B.V.

Fluorine-Rich Planetary Environments as Possible Habitats for Life

PubMed Central

Budisa, Nediljko; Kubyshkin, Vladimir; Schulze-Makuch, Dirk

2014-01-01

In polar aprotic organic solvents, fluorine might be an element of choice for life that uses selected fluorinated building blocks as monomers of choice for self-assembling of its catalytic polymers. Organofluorine compounds are extremely rare in the chemistry of life as we know it. Biomolecules, when fluorinated such as peptides or proteins, exhibit a “fluorous effect”, i.e., they are fluorophilic (neither hydrophilic nor lipophilic). Such polymers, capable of creating self-sorting assemblies, resist denaturation by organic solvents by exclusion of fluorocarbon side chains from the organic phase. Fluorous cores consist of a compact interior, which is shielded from the surrounding solvent. Thus, we can anticipate that fluorine-containing “teflon”-like or “non-sticking” building blocks might be monomers of choice for the synthesis of organized polymeric structures in fluorine-rich planetary environments. Although no fluorine-rich planetary environment is known, theoretical considerations might help us to define chemistries that might support life in such environments. For example, one scenario is that all molecular oxygen may be used up by oxidation reactions on a planetary surface and fluorine gas could be released from F-rich magma later in the history of a planetary body to result in a fluorine-rich planetary environment. PMID:25370378

Inhibiting nucleation of amyloid structure in a huntingtin fragment by targeting α-helix rich oligomeric intermediates

PubMed Central

Mishra, Rakesh; Jayaraman, Murali; Roland, Bartholomew P.; Landrum, Elizabeth; Fullam, Timothy; Kodali, Ravindra; Thakur, Ashwani K.; Arduini, Irene; Wetzel, Ronald

2011-01-01

Although oligomeric intermediates are transiently formed in almost all known amyloid assembly reactions, their mechanistic roles are poorly understood. Recently we demonstrated a critical role for the 17 amino acid N-terminal segment (httNT) of huntingtin (htt) in oligomer-mediated amyloid assembly of htt N-terminal fragments. In this mechanism, the httNT segment forms the α-helix rich core of the oligomers, leaving most or all of each polyglutamine (polyQ) segment disordered and solvent-exposed. Nucleation of amyloid structure occurs within this local high concentration of disordered polyQ. Here we demonstrate the kinetic importance of httNT self-assembly by describing inhibitory httNT-containing peptides that appear to work by targeting nucleation within the oligomer fraction. These molecules inhibit amyloid nucleation by forming mixed oligomers with the httNT domains of polyQ-containing htt N-terminal fragments. In one class of inhibitor, nucleation is passively suppressed due to the reduced local concentration of polyQ within the mixed oligomer. In the other class, nucleation is actively suppressed by a proline-rich polyQ segment covalently attached to httNT. Studies with D-amino acid and scrambled sequence versions of httNT suggest that inhibition activity is strongly linked to the propensity of inhibitory peptides to make amphipathic α-helices. HttNT derivatives with C-terminal cell penetrating peptide segments, also exhibit excellent inhibitory activity. The httNT-based peptides described here, especially those with protease-resistant D-amino acids and/or with cell penetrating sequences, may prove useful as lead therapeutics for inhibiting nucleation of amyloid formation in Huntington’s disease. PMID:22178478

Trichloroethylene-mediated cytotoxicity in human epidermal keratinocytes is mediated by the rapid accumulation of intracellular calcium: Interception by naringenin.

PubMed

Ali, F; Khan, A Q; Khan, R; Sultana, S

2016-02-01

Industrial solvents pose a significant threat to the humankind. The mechanisms of their toxicity still remain in debate. Trichloroethylene (TCE) is a widespread industrial solvent responsible for severe liver dysfunction, cutaneous toxicity in occupationally exposed humans. We utilized an in vitro system of human epidermal keratinocyte (HaCaT) cells in this study to avoid complex cell and extracellular interactions. We report the cytotoxicity of organic solvent TCE in HaCaT and its reversal by a natural flavanone, naringenin (Nar). The cytotoxicity was attributed to the rapid intracellular free calcium (Ca(2+)) release, which might lead to the elevation of protein kinase C along with robust free radical generation, instability due to energy depletion, and sensitization of intracellular stress signal transducer nuclear factor κB. These effects were actually seen to induce significant amount of genomic DNA fragmentation. Furthermore, all these effects of TCE were effectively reversed by the treatment of Nar, a natural flavanone. Our studies identify intracellular Ca as a unique target used by organic solvents in the cytotoxicity and highlight the Ca(2+) ion stabilizer properties of Nar. © The Author(s) 2015.

Toward understanding of the mechanisms of Mediator function in vivo: Focus on the preinitiation complex assembly.

PubMed

Eychenne, Thomas; Werner, Michel; Soutourina, Julie

2017-01-01

Mediator is a multisubunit complex conserved in eukaryotes that plays an essential coregulator role in RNA polymerase (Pol) II transcription. Despite intensive studies of the Mediator complex, the molecular mechanisms of its function in vivo remain to be fully defined. In this review, we will discuss the different aspects of Mediator function starting with its interactions with specific transcription factors, its recruitment to chromatin and how, as a coregulator, it contributes to the assembly of transcription machinery components within the preinitiation complex (PIC) in vivo and beyond the PIC formation.

Tailoring the Variational Implicit Solvent Method for New Challenges: Biomolecular Recognition and Assembly

PubMed Central

Ricci, Clarisse Gravina; Li, Bo; Cheng, Li-Tien; Dzubiella, Joachim; McCammon, J. Andrew

2018-01-01

Predicting solvation free energies and describing the complex water behavior that plays an important role in essentially all biological processes is a major challenge from the computational standpoint. While an atomistic, explicit description of the solvent can turn out to be too expensive in large biomolecular systems, most implicit solvent methods fail to capture “dewetting” effects and heterogeneous hydration by relying on a pre-established (i.e., guessed) solvation interface. Here we focus on the Variational Implicit Solvent Method, an implicit solvent method that adds water “plasticity” back to the picture by formulating the solvation free energy as a functional of all possible solvation interfaces. We survey VISM's applications to the problem of molecular recognition and report some of the most recent efforts to tailor VISM for more challenging scenarios, with the ultimate goal of including thermal fluctuations into the framework. The advances reported herein pave the way to make VISM a uniquely successful approach to characterize complex solvation properties in the recognition and binding of large-scale biomolecular complexes. PMID:29484300

Deposition dynamics of multi-solvent bioinks

NASA Astrophysics Data System (ADS)

Kaneelil, Paul; Pack, Min; Cui, Chunxiao; Han, Li-Hsin; Sun, Ying

2017-11-01

Inkjet printing cellular scaffolds using bioinks is gaining popularity due to the advancement of printing technology as well as the growing demands of regenerative medicine. Numerous studies have been conducted on printing scaffolds of biomimetic structures that support the cell production of human tissues. However, the underlying physics of the deposition dynamics of bioinks remains elusive. Of particular interest is the unclear deposition dynamics of multi-solvent bioinks, which is often used to tune the micro-architecture formation. Here we systematically studied the effects of jetting frequency, solvent properties, substrate wettability, and temperature on the three-dimensional deposition patterns of bioinks made of Methacrylated Gelatin and Carboxylated Gelatin. The microflows inside the inkjet-printed picolitre drops were visualized using fluorescence tracer particles to decipher the complex processes of multi-solvent evaporation and solute self-assembly. The evolution of droplet shape was observed using interferometry. With the integrated techniques, the interplay of solvent evaporation, biopolymer deposition, and multi-drop interactions were directly observed for various ink and substrate properties, and printing conditions. Such knowledge enables the design and fabrication of a variety of tissue engineering scaffolds for potential use in regenerative medicine.

Solvent extraction: the coordination chemistry behind extractive metallurgy.

PubMed

Wilson, A Matthew; Bailey, Phillip J; Tasker, Peter A; Turkington, Jennifer R; Grant, Richard A; Love, Jason B

2014-01-07

The modes of action of the commercial solvent extractants used in extractive hydrometallurgy are classified according to whether the recovery process involves the transport of metal cations, M(n+), metalate anions, MXx(n-), or metal salts, MXx into a water-immiscible solvent. Well-established principles of coordination chemistry provide an explanation for the remarkable strengths and selectivities shown by most of these extractants. Reagents which achieve high selectivity when transporting metal cations or metal salts into a water-immiscible solvent usually operate in the inner coordination sphere of the metal and provide donor atom types or dispositions which favour the formation of particularly stable neutral complexes that have high solubility in the hydrocarbons commonly used in recovery processes. In the extraction of metalates, the structures of the neutral assemblies formed in the water-immiscible phase are usually not well defined and the cationic reagents can be assumed to operate in the outer coordination spheres. The formation of secondary bonds in the outer sphere using, for example, electrostatic or H-bonding interactions are favoured by the low polarity of the water-immiscible solvents.

Water droplets as template for next-generation self-assembled poly-(etheretherketone) with cardo membranes.

PubMed

Gugliuzza, Annarosa; Aceto, Marianna Carmela; Macedonio, Francesca; Drioli, Enrico

2008-08-28

Next generation PEEK-WC membranes have been fabricated by using an innovative self-assembly technique. Patterned architectures have been achieved via a solvent-reduced and water-assisted process, resulting in honeycomb packed geometry. The membranes exhibit monodisperse pores with size and shape comparable to those left by templating water droplets. Influencing factors for the formation of self-assembled poly-(etheretherketone) with Cardo [PEEK-WC] membranes have been evaluated, identifying the critical parameters for nucleation, growth, and propagation of the droplet-mobile arrays through the overall films. Structure-transport relationships have been discussed according to the results achieved from the implementation of membrane distillation processes, yielding indication about the suitability of self-assembled PEEK-WC films to work as interfaces in contactor operations.

Self-Assembled Pyridine-Dipyrrolate Cages.

PubMed

Zhang, Huacheng; Lee, Juhoon; Lammer, Aaron D; Chi, Xiaodong; Brewster, James T; Lynch, Vincent M; Li, Hao; Zhang, Zhan; Sessler, Jonathan L

2016-04-06

An inherently nonlinear pyridine dipyrrolate ligand, namely 2,6-bis(3,4-diethyl-5-carboxy-1H-pyrrol-2yl)pyridine (compound 1), is able to distinguish between different zinc(II) cation sources, namely Zn(acac)2 and Zn(OAc)2, respectively. This differentiation is manifest both in terms of the observed fluorescent behavior in mixed organic media and the reaction chemistry. Treatment of 1 with Zn(acac)2 gives rise to a cage dimer, cage-1, wherein two molecules of compound 1 act as double bridging units to connect two individual cage subunits. As inferred from X-ray crystallographic studies, this cage system consists of discrete zinc dimers with hydroxide bridges that, with the assistance of bound DMF solvent molecules, serve to fix the geometry and orientation of the pyridine dipyrrolate building blocks. When a different zinc source, Zn(OAc)2, is used to carry out an ostensibly similar complexation reaction with compound 1, an acetate-bridged 1D abacus-like cage polymer is obtained as inferred from X-ray diffraction analysis. This extended solid state structure, cage-2, contains individual zinc dimer cage submits and appears stabilized by solvent molecules (DMF) and the counteranion (acetate). Rod-like assemblies are also observed by DLS and SEM. This construct, in contrast to cage-1, proved fluorescent in mixed organic media. The structure of the ligand itself (i.e., in the absence of Zn(II)) was confirmed by X-ray crystallographic analysis and was found to assemble into a supramolecular polymer. Conversion to a dimer form was seen upon the addition of TBAOAc. On the basis of the metric parameters, the structures seen in the solid state are stabilized via hydrogen bonding interactions involving solvent molecules.

Hierarchical nanoparticle assemblies formed by decorating breath figures.

PubMed

Böker, Alexander; Lin, Yao; Chiapperini, Kristen; Horowitz, Reina; Thompson, Mike; Carreon, Vincent; Xu, Ting; Abetz, Clarissa; Skaff, Habib; Dinsmore, A D; Emrick, Todd; Russell, Thomas P

2004-05-01

The combination of two self-assembly processes on different length scales leads to the formation of hierarchically structured nanoparticle arrays. Here, the formation of spherical cavities, or 'breath figures'-made by the condensation of micrometre-sized water droplets on the surface of a polymer solution-that self-assemble into a well-ordered hexagonal array, is combined with the self-assembly of CdSe nanoparticles at the polymer solution-water droplet interface. Complete evaporation of the solvent and water confines the particle assembly to an array of spherical cavities and allows for ex situ investigation. Fluorescence confocal, transmission electron and scanning electron microscope images show the preferential segregation of the CdSe nanoparticles to the polymer solution-water interface where they form a 5-7-nm-thick layer, thus functionalizing the walls of the holes. This process opens a new route to fabricating highly functionalized ordered microarrays of nanoparticles, potentially useful in sensory, separation membrane or catalytic applications.

Tuning carbon nanotube assembly for flexible, strong and conductive films.

PubMed

Wang, Yanjie; Li, Min; Gu, Yizhuo; Zhang, Xiaohua; Wang, Shaokai; Li, Qingwen; Zhang, Zuoguang

2015-02-21

Carbon nanotubes are ideal scaffolds for designing and architecting flexible graphite films with tunable mechanical, electrical and thermal properties. Herein, we demonstrate that the assembly of aligned carbon nanotubes with different aggregation density and morphology leads to different mechanical properties and anisotropic electrical conduction along the films. Using drying evaporation under tension treatment, the carbon nanotubes can be assembled into strong films with tensile strength and Young's modulus as high as 3.2 GPa and 124 GPa, respectively, leading to a remarkable toughness of 54.38 J g(-1), greatly outperforming conventional graphite films, spider webs and even Kevlar fiber films. Different types of solvents may result in the assembly of CNTs with different aggregation morphology and therefore different modulus. In addition, we reveal that the high density assembly of aligned CNTs correlates with better electric conduction along the axial direction, enabling these flexible graphite films to be both strong and conductive.

Continuous Flow Science in an Undergraduate Teaching Laboratory: Bleach-Mediated Oxidation in a Biphasic System

ERIC Educational Resources Information Center

Kairouz, Vanessa; Collins, Shawn K.

2018-01-01

An undergraduate teaching laboratory experiment involving a continuous flow, bleach-mediated oxidation of aldehydes under biphasic conditions was developed that allowed students to explore concepts of mixing or mass transport, solvent sustainability, biphasic reactions, phase transfer catalysis, and continuous flow chemistry.

In vitro reconstitution of chaperone-mediated human RISC assembly.

PubMed

Naruse, Ken; Matsuura-Suzuki, Eriko; Watanabe, Mariko; Iwasaki, Shintaro; Tomari, Yukihide

2018-01-01

To silence target mRNAs, small RNAs and Argonaute (Ago) proteins need to be assembled into RNA-induced silencing complexes (RISCs). Although the assembly of Drosophila melanogaster RISC was recently reconstituted by Ago2, the Dicer-2/R2D2 heterodimer, and five chaperone proteins, the absence of a reconstitution system for mammalian RISC assembly has posed analytical challenges. Here we describe reconstitution of human RISC assembly using Ago2 and five recombinant chaperone proteins: Hsp90β, Hsc70, Hop, Dnaja2, and p23. Our data show that ATP hydrolysis by both Hsp90β and Hsc70 is required for RISC assembly of small RNA duplexes but not for that of single-stranded RNAs. The reconstitution system lays the groundwork for further studies of small RNA-mediated gene silencing in mammals. © 2018 Naruse et al.; Published by Cold Spring Harbor Laboratory Press for the RNA Society.

Self-assembly in solvates of 2,4-diamino-6-(4-methyl- phenyl)-1,3,5-triazine and in its molecular adducts with some aliphatic dicarboxylic acids

NASA Astrophysics Data System (ADS)

Nandy, Purnendu; Nayak, Amrita; Biswas, Sharmita Nandy; Pedireddi, V. R.

2016-03-01

Solid state structures of 2,4-diamino-6-(4-methylphenyl)-1,3,5-triazine, 1, in the form of methanol and dimethylsulfoxide (DMSO) solvates, as well as supramolecular assemblies of 1 with various aliphatic dicarboxylic acids, oxalic (a), malonic (b), succinic (c), glutaric (d) and adipic (e) have been reported. Analysis of the assemblies has been carried out by single crystal X-ray diffraction and thermal methods. Triazine 1 yields anhydrous molecular adducts with acids a-d, upon co-crystallization either from CH3OH and DMSO solvents. However acid e gives anhydrous adduct from DMSO solvent, while it gives a methanol adduct from CH3OH. Structure determination reveals that molecular adducts 1a, 1d and 1e are in a 2:1 ratio of 1 and the corresponding acid. However the ratio is 1:1, in 1b, perhaps due to the involvement of one of the acid groups in the intramolecular hydrogen bonding and in adduct 1c the ratio observed is 3:2. Structural features in all these assemblies have been rationalised in terms of various recognition patterns formed between the acceptor and donor groups. A noteworthy feature is that -COOH groups in acid a establish interaction with 1 through amino groups, while such interactions are observed to be through hetero -N atoms in case of the acids b-e.

Mediator directs co-transcriptional heterochromatin assembly by RNA interference-dependent and -independent pathways.

PubMed

Oya, Eriko; Kato, Hiroaki; Chikashige, Yuji; Tsutsumi, Chihiro; Hiraoka, Yasushi; Murakami, Yota

2013-01-01

Heterochromatin at the pericentromeric repeats in fission yeast is assembled and spread by an RNAi-dependent mechanism, which is coupled with the transcription of non-coding RNA from the repeats by RNA polymerase II. In addition, Rrp6, a component of the nuclear exosome, also contributes to heterochromatin assembly and is coupled with non-coding RNA transcription. The multi-subunit complex Mediator, which directs initiation of RNA polymerase II-dependent transcription, has recently been suggested to function after initiation in processes such as elongation of transcription and splicing. However, the role of Mediator in the regulation of chromatin structure is not well understood. We investigated the role of Mediator in pericentromeric heterochromatin formation and found that deletion of specific subunits of the head domain of Mediator compromised heterochromatin structure. The Mediator head domain was required for Rrp6-dependent heterochromatin nucleation at the pericentromere and for RNAi-dependent spreading of heterochromatin into the neighboring region. In the latter process, Mediator appeared to contribute to efficient processing of siRNA from transcribed non-coding RNA, which was required for efficient spreading of heterochromatin. Furthermore, the head domain directed efficient transcription in heterochromatin. These results reveal a pivotal role for Mediator in multiple steps of transcription-coupled formation of pericentromeric heterochromatin. This observation further extends the role of Mediator to co-transcriptional chromatin regulation.

Novel approaches mediated by tailor-made green solvents for the extraction of phenolic compounds from agro-food industrial by-products.

PubMed

Fernández, María de Los Ángeles; Espino, Magdalena; Gomez, Federico J V; Silva, María Fernanda

2018-01-15

An environmentally friendly method for the phenolic compound extraction from agro-food industrial by-products was developed in order to contribute with their sustainable valorization. A Natural Deep Eutectic Solvent was chemometrically-designed for the first time and compared with traditional solvents in terms of analyte stabilization. The combination of lactic acid, glucose and 15% water (LGH-15) was selected as optimal. A high-efficiency ultrasound-assisted extraction mediated by LGH-15 prior to HPLC-DAD allows the determination of 14 phenols in onion, olive, tomato and pear industrial by-products. NADES synthesis as well as the extraction procedures were optimized by Response Surface Methodology. Thus, phenolic determination in these complex samples was achieved by a simple, non-expensive, eco-friendly and robust system. The application to different matrices demonstrated the versatility of the proposed method. NADES opens interesting perspectives for their potential use as vehicles of bioactive compounds as food additives or pharmaceuticals. Copyright © 2017 Elsevier Ltd. All rights reserved.

Inter and Intra Molecular Phase Separation Environment Effects on PI-PEO Block Copolymers for Batteries and Fuel Cells

NASA Technical Reports Server (NTRS)

Xue, Chen-Chen; Meador, Mary Ann B.; Eby, R. K.; Cheng, Stephen Z. D.; Ge, Jason J.; Cubon, Valerie A.

2002-01-01

Rod-coil molecules have been introduced as a novel type of block copolymers with unique microstructure due to their ability to self-assemble to various ordered morphologies on a nanometer length scale. These molecules, comprised two homo polymers joined together at one end, microphase separate into ordered, periodic arrays of spheres, cylinders in the bulk state and or solution. To get ordered structure in a reasonable scale, additional force field are applied, such as mechanical shearing, electric field and magnetic field. Recently, progress has made it a possible to develop a new class of polyimides (PI)-Polyethylene oxide (PEO) that are soluble in polar organic solvents. The solvent-soluble PI-PEO has a wide variety of applications in microelectronics, since these PI-PEO films exhibit a high degree of thermal and chemical stability. In this paper, we report the self-assembled ordered structure of PI-PEO molecules formed from concentrate solution.

Biobased Fat Mimicking Molecular Structuring Agents for Medium-Chain Triglycerides (MCTs) and Other Edible Oils.

PubMed

Silverman, Julian R; John, George

2015-12-09

To develop sustainable value-added materials from biomass, novel small-molecule sugar ester gelators were synthesized using biocatalysis. The facile one-step regiospecific coupling of the pro-antioxidant raspberry ketone glucoside and unsaturated or saturated long- and medium-chain fatty acids provides a simple approach to tailor the structure and self-assembly of the amphiphilic product. These low molecular weight molecules demonstrated the ability to self-assemble in a variety of solvents and exhibited supergelation, with a minimum gelation concentration of 0.25 wt %, in numerous organic solvents, as well as in a range of natural edible oils, specifically a relatively unstudied group of liquids: natural medium-chain triglyceride oils, notably coconut oil. Spectroscopic analysis details the gelator structure as well as the intermolecular noncovalent interactions, which allow for gelation. X-ray diffraction studies indicate fatty acid chain packing of gelators is similar to that of natural fats, signifying the crystalline nature may lead to desirable textural properties and mouthfeel.

Size and space controlled hexagonal arrays of superparamagnetic iron oxide nanodots: magnetic studies and application

PubMed Central

Ghoshal, Tandra; Maity, Tuhin; Senthamaraikannan, Ramsankar; Shaw, Matthew T.; Carolan, Patrick; Holmes, Justin D.; Roy, Saibal; Morris, Michael A.

2013-01-01

Highly dense hexagonally arranged iron oxide nanodots array were fabricated using PS-b-PEO self-assembled patterns. The copolymer molecular weight, composition and choice of annealing solvent/s allows dimensional and structural control of the nanopatterns at large scale. A mechanism is proposed to create scaffolds through degradation and/or modification of cylindrical domains. A methodology based on selective metal ion inclusion and subsequent processing was used to create iron oxide nanodots array. The nanodots have uniform size and shape and their placement mimics the original self-assembled nanopatterns. For the first time these precisely defined and size selective systems of ordered nanodots allow careful investigation of magnetic properties in dimensions from 50 nm to 10 nm, which delineate the nanodots are superparamagnetic, well-isolated and size monodispersed. This diameter/spacing controlled iron oxide nanodots systems were demonstrated as a resistant mask over silicon to fabricate densely packed, identical ordered, high aspect ratio silicon nanopillars and nanowire features. PMID:24072037

A priori calculations of the free energy of formation from solution of polymorphic self-assembled monolayers.

PubMed

Reimers, Jeffrey R; Panduwinata, Dwi; Visser, Johan; Chin, Yiing; Tang, Chunguang; Goerigk, Lars; Ford, Michael J; Sintic, Maxine; Sum, Tze-Jing; Coenen, Michiel J J; Hendriksen, Bas L M; Elemans, Johannes A A W; Hush, Noel S; Crossley, Maxwell J

2015-11-10

Modern quantum chemical electronic structure methods typically applied to localized chemical bonding are developed to predict atomic structures and free energies for meso-tetraalkylporphyrin self-assembled monolayer (SAM) polymorph formation from organic solution on highly ordered pyrolytic graphite surfaces. Large polymorph-dependent dispersion-induced substrate-molecule interactions (e.g., -100 kcal mol(-1) to -150 kcal mol(-1) for tetratrisdecylporphyrin) are found to drive SAM formation, opposed nearly completely by large polymorph-dependent dispersion-induced solvent interactions (70-110 kcal mol(-1)) and entropy effects (25-40 kcal mol(-1) at 298 K) favoring dissolution. Dielectric continuum models of the solvent are used, facilitating consideration of many possible SAM polymorphs, along with quantum mechanical/molecular mechanical and dispersion-corrected density functional theory calculations. These predict and interpret newly measured and existing high-resolution scanning tunnelling microscopy images of SAM structure, rationalizing polymorph formation conditions. A wide range of molecular condensed matter properties at room temperature now appear suitable for prediction and analysis using electronic structure calculations.

Layer-by-layer assembled biopolymer microcapsule with separate layer cavities generated by gas-liquid microfluidic approach.

PubMed

Wang, Yifeng; Zhou, Jing; Guo, Xuecheng; Hu, Qian; Qin, Chaoran; Liu, Hui; Dong, Meng; Chen, Yanjun

2017-12-01

In this work, a layer-by-layer (LbL) assembled biopolymer microcapsule with separate layer cavities is generated by a novel and convenient gas-liquid microfluidic approach. This approach exhibits combined advantages of microfluidic approach and LbL assembly method, and it can straightforwardly build LbL-assembled capsules in mild aqueous environments at room temperature. In particular, using this approach we can build the polyelectrolyte multilayer capsule with favorable cavities in each layer, and without the need for organic solvent, emulsifying agent, or sacrificial template. Various components (e.g., drugs, proteins, fluorescent dyes, and nanoparticles) can be respectively encapsulated in the separate layer cavities of the LbL-assembled capsules. Moreover, the encapsulated capsules present the ability as colorimetric sensors, and they also exhibit the interesting release behavior. Therefore, the LbL-assembled biopolymer capsule is a promising candidate for biomedical applications in targeted delivery, controlled release, and bio-detection. Copyright © 2017 Elsevier B.V. All rights reserved.

Hierarchical self-assembly of a bow-shaped molecule bearing self-complementary hydrogen bonding sites into extended supramolecular assemblies.

PubMed

Ikeda, Masato; Nobori, Tadahito; Schmutz, Marc; Lehn, Jean-Marie

2005-01-07

The bow-shaped molecule 1 bearing a self-complementary DAAD-ADDA (D=donor A=acceptor) hydrogen-bonding array generates, in hydrocarbon solvents, highly ordered supramolecular sheet aggregates that subsequently give rise to gels by formation of an entangled network. The process of hierarchical self-assembly of compound 1 was investigated by the concentration and temperature dependence of UV-visible and (1)H NMR spectra, fluorescence spectra, and electron microscopy data. The temperature dependence of the UV-visible spectra indicates a highly cooperative process for the self-assembly of compound 1 in decaline. The electron micrograph of the decaline solution of compound 1 (1.0 mM) revealed supramolecular sheet aggregates forming an entangled network. The selected area electronic diffraction patterns of the supramolecular sheet aggregates were typical for single crystals, indicative of a highly ordered assembly. The results exemplify the generation, by hierarchical self-assembly, of highly organized supramolecular materials presenting novel collective properties at each level of organization.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Holt, Allison M; Standaert, Robert F; Jubb, Aaron M

Biological membranes, formed primarily by the self-assembly of complex mixtures of phospholipids, provide a structured scaffold for compartmentalization and structural processes in living cells. The specific physical properties of phospholipid species present in a given membrane play a key role in mediating these processes. Phosphatidylethanolamine (PE), a zwitterionic lipid present in bacterial, yeast, and mammalian cell membranes, is exceptional. In addition to undergoing the standard lipid polymorphic transition between the gel and liquid-crystalline phase, it can also assume an unusual polymorphic state, the inverse hexagonal phase (HII). Divalent cations are among the factors that drive the formation of the HIImore » phase, wherein the lipid molecules form stacked tubular structures by burying the hydrophilic head groups and exposing the hydrophobic tails to the bulk solvent. Most biological membranes contain a lipid species capable of forming the HII state suggesting that such lipid polymorphic structural states play an important role in structural biological processes such as membrane fusion. In this study, the interactions between Mg2+ and biomimetic bacterial cell membranes composed of PE and phosphatidylglycerol (PG) were probed using differential scanning calorimetry (DSC), small-angle x-ray scattering (SAXS), and fluorescence spectroscopy. The lipid phase transitions were examined at varying ratios of PE to PG and upon exposure to physiologically relevant concentrations of Mg2+. An understanding of these basic interactions enhances our understanding of membrane dynamics and how membrane-mediated structural changes may occur in vivo.« less

Phosphotyrosine-mediated LAT assembly on membranes drives kinetic bifurcation in recruitment dynamics of the Ras activator SOS

DOE PAGES

Huang, William Y. C.; Yan, Qingrong; Lin, Wan-Chen; ...

2016-07-01

The assembly of cell surface receptors with downstream signaling molecules is a commonly occurring theme in multiple signaling systems. However, little is known about how these assemblies modulate reaction kinetics and the ultimate propagation of signals. Here, we reconstitute phosphotyrosine-mediated assembly of extended linker for the activation of T cells (LAT):growth factor receptor-bound protein 2 (Grb2):Son of Sevenless (SOS) networks, derived from the T-cell receptor signaling system, on supported membranes. Single-molecule dwell time distributions reveal two, well-differentiated kinetic species for both Grb2 and SOS on the LAT assemblies. The majority fraction of membrane-recruited Grb2 and SOS both exhibit fast kineticsmore » and single exponential dwell time distributions, with average dwell times of hundreds of milliseconds. The minor fraction exhibits much slower kinetics, extending the dwell times to tens of seconds. Considering this result in the context of the multistep process by which the Ras GEF (guanine nucleotide exchange factor) activity of SOS is activated indicates that kinetic stabilization from the LAT assembly may be important. This kinetic proofreading effect would additionally serve as a stochastic noise filter by reducing the relative probability of spontaneous SOS activation in the absence of receptor triggering. In conclusion, the generality of receptor-mediated assembly suggests that such effects may play a role in multiple receptor proximal signaling processes.« less

Phosphotyrosine-mediated LAT assembly on membranes drives kinetic bifurcation in recruitment dynamics of the Ras activator SOS

PubMed Central

Huang, William Y. C.; Yan, Qingrong; Lin, Wan-Chen; Chung, Jean K.; Hansen, Scott D.; Christensen, Sune M.; Tu, Hsiung-Lin; Kuriyan, John; Groves, Jay T.

2016-01-01

The assembly of cell surface receptors with downstream signaling molecules is a commonly occurring theme in multiple signaling systems. However, little is known about how these assemblies modulate reaction kinetics and the ultimate propagation of signals. Here, we reconstitute phosphotyrosine-mediated assembly of extended linker for the activation of T cells (LAT):growth factor receptor-bound protein 2 (Grb2):Son of Sevenless (SOS) networks, derived from the T-cell receptor signaling system, on supported membranes. Single-molecule dwell time distributions reveal two, well-differentiated kinetic species for both Grb2 and SOS on the LAT assemblies. The majority fraction of membrane-recruited Grb2 and SOS both exhibit fast kinetics and single exponential dwell time distributions, with average dwell times of hundreds of milliseconds. The minor fraction exhibits much slower kinetics, extending the dwell times to tens of seconds. Considering this result in the context of the multistep process by which the Ras GEF (guanine nucleotide exchange factor) activity of SOS is activated indicates that kinetic stabilization from the LAT assembly may be important. This kinetic proofreading effect would additionally serve as a stochastic noise filter by reducing the relative probability of spontaneous SOS activation in the absence of receptor triggering. The generality of receptor-mediated assembly suggests that such effects may play a role in multiple receptor proximal signaling processes. PMID:27370798

Phosphotyrosine-mediated LAT assembly on membranes drives kinetic bifurcation in recruitment dynamics of the Ras activator SOS.

PubMed

Huang, William Y C; Yan, Qingrong; Lin, Wan-Chen; Chung, Jean K; Hansen, Scott D; Christensen, Sune M; Tu, Hsiung-Lin; Kuriyan, John; Groves, Jay T

2016-07-19

The assembly of cell surface receptors with downstream signaling molecules is a commonly occurring theme in multiple signaling systems. However, little is known about how these assemblies modulate reaction kinetics and the ultimate propagation of signals. Here, we reconstitute phosphotyrosine-mediated assembly of extended linker for the activation of T cells (LAT):growth factor receptor-bound protein 2 (Grb2):Son of Sevenless (SOS) networks, derived from the T-cell receptor signaling system, on supported membranes. Single-molecule dwell time distributions reveal two, well-differentiated kinetic species for both Grb2 and SOS on the LAT assemblies. The majority fraction of membrane-recruited Grb2 and SOS both exhibit fast kinetics and single exponential dwell time distributions, with average dwell times of hundreds of milliseconds. The minor fraction exhibits much slower kinetics, extending the dwell times to tens of seconds. Considering this result in the context of the multistep process by which the Ras GEF (guanine nucleotide exchange factor) activity of SOS is activated indicates that kinetic stabilization from the LAT assembly may be important. This kinetic proofreading effect would additionally serve as a stochastic noise filter by reducing the relative probability of spontaneous SOS activation in the absence of receptor triggering. The generality of receptor-mediated assembly suggests that such effects may play a role in multiple receptor proximal signaling processes.

Amphiphilic invertible polymers: Self-assembly into functional materials driven by environment polarity

NASA Astrophysics Data System (ADS)

Hevus, Ivan

Stimuli-responsive polymers adapt to environmental changes by adjusting their chain conformation in a fast and reversible way. Responsive polymeric materials have already found use in electronics, coatings industry, personal care, and bio-related areas. The current work aims at the development of novel responsive functional polymeric materials by manipulating environment-dependent self-assembly of a new class of responsive macromolecules strategically designed in this study,—amphiphilic invertible polymers (AIPs). Environment-dependent micellization and self-assembly of three different synthesized AIP types based on poly(ethylene glycol) as a hydrophilic fragment and varying hydrophobic constituents was demonstrated in polar and nonpolar solvents, as well as on the surfaces and interfaces. With increasing concentration, AIP micelles self-assemble into invertible micellar assemblies composed of hydrophilic and hydrophobic domains. Polarity-responsive properties of AIPs make invertible micellar assemblies functional in polar and nonpolar media including at interfaces. Thus, invertible micellar assemblies solubilize poorly soluble substances in their interior in polar and nonpolar solvents. In a polar aqueous medium, a novel stimuli-responsive mechanism of drug release based on response of AIP-based drug delivery system to polarity change upon contact with the target cell has been established using invertible micellar assemblies loaded with curcumin, a phytochemical drug. In a nonpolar medium, invertible micellar assemblies were applied simultaneously as nanoreactors and stabilizers for size-controlled synthesis of silver nanoparticles stable in both polar and nonpolar media. The developed amphiphilic nanosilver was subsequently used as seeds to promote anisotropic growth of CdSe semiconductor nanoparticles that have potential in different applications ranging from physics to medicine. Amphiphilic invertible polymers were shown to adsorb on the surface of silica nanoparticles strongly differing in polarity. AIP modified silica nanoparticles are able to adsolubilize molecules of poorly water-soluble 2-naphthol into the adsorbed polymer layer. The adsolubilization ability of adsorbed invertible macromolecules makes AIP-modified silica nanoparticles potentially useful in wastewater treatment or biomedical applications. Finally, the invertible micellar assemblies were used as functional additives to improve the appearance of electrospun silicon wires based on cyclohexasilane, a liquid silicon precursor. AIP-assisted fabrication of silicon wires from the liquid cyclohexasilane precursor has potential as a scalable method for developing electronic functional materials.

Block Copolymer Micelles as Nanocontainers for Controlled Release of Proteins from Biocompatible Oil Phases

PubMed Central

2009-01-01

Biocompatible oils are used in a variety of medical applications ranging from vaccine adjuvants to vehicles for oral drug delivery. To enable such nonpolar organic phases to serve as reservoirs for delivery of hydrophilic compounds, we explored the ability of block copolymer micelles in organic solvents to sequester proteins for sustained release across an oil−water interface. Self-assembly of the block copolymer, poly(ϵ-caprolactone)-block-poly(2-vinyl pyridine) (PCL-b-P2VP), was investigated in toluene and oleic acid, a biocompatible naturally occurring fatty acid. Micelle formation in toluene was characterized by dynamic light scattering (DLS) and atomic force microscopy (AFM) imaging of micelles cast onto silicon substrates. Cryogenic transmission electron microscopy confirmed a spherical morphology in oleic acid. Studies of homopolymer solubility implied that micelles in oleic acid consist of a P2VP corona and a PCL core, while P2VP formed the core of micelles assembled in toluene. The loading of two model proteins (ovalbumin (ova) and bovine serum albumin (BSA)) into micelles was demonstrated with loadings as high as 7.8% wt of protein per wt of P2VP in oleic acid. Characterization of block copolymer morphology in the two solvents after protein loading revealed spherical particles with similar size distributions to the as-assembled micelles. Release of ova from micelles in oleic acid was sustained for 12−30 h upon placing the oil phase in contact with an aqueous bath. Unique to the situation of micelle assembly in an oily phase, the data suggest protein is sequestered in the P2VP corona block of PCL-b-P2VP micelles in oleic acid. More conventionally, protein loading occurs in the P2VP core of micelles assembled in toluene. PMID:19235932

Molybdenum-oxide based unique polyprotic nanoacids showing different deprotonations and related assembly processes in solution.

PubMed

Kistler, Melissa L; Liu, Tianbo; Gouzerh, Pierre; Todea, Ana Maria; Müller, Achim

2009-07-14

We report the self-assembly processes in solution of three Keplerate-type molybdenum-oxide based clusters {Mo72V30}, {Mo72Cr30} and {Mo72Fe30} (all with diameters of approximately 2.5 nm). These clusters behave as unique weak polyprotic acids owing to the external water ligands attached to the non-Mo metal centers. Whereas the Cr and Fe clusters have 30 water ligands attached at the 30 M3+ centers pointing outside, {Mo72V30} has 20 water ligands coordinated to vanadium atoms, of which only 10 are pointing outside. The self-assembly processes of the Keplerates leading to supramolecular blackberry-type structures are influenced by the effective charge densities on the cluster surfaces, which can be tuned by the pH values and solvent properties. As expected, {Mo72Cr30} and {Mo72Fe30} behave similarly in aqueous solution due to their analogous structures and in both cases the self-assembly follows the partial deprotonation of the external water ligands attached to the non-Mo metal centers. However, the M-OH2 functionalities differ not only in acidity but also lability, i.e. in different residence times of the H2O ligands. In contrast to {Mo72Cr30} and {Mo72Fe30}, the {Mo72V30} clusters carry a rather large number of negative charges so that their solution properties are different. They exist as discrete macroions in dilute aqueous solution, and form only in mixed water/organic solvent (like acetone) blackberry-type structures whose size increases with acetone content. The comparison of the properties of the clusters allows more general information about the interesting self-assembly phenomenon to be unveiled.

Indium-mediated asymmetric barbier-type allylations: additions to aldehydes and ketones and mechanistic investigation of the organoindium reagents.

PubMed

Haddad, Terra D; Hirayama, Lacie C; Singaram, Bakthan

2010-02-05

We report a simple, efficient, and general method for the indium-mediated enantioselective allylation of aromatic and aliphatic aldehydes and ketones under Barbier-type conditions in a one-pot synthesis affording the corresponding chiral alcohol products in very good yield (up to 99%) and enantiomeric excess (up to 93%). Our method is able to tolerate various functional groups, such as esters, nitriles, and phenols. Additionally, more substituted allyl bromides, such as crotyl and cinnamyl bromide, can be used providing moderate enantioselectivity (72% and 56%, respectively) and excellent diastereoselectivity when employing cinnamyl bromide (>95/5 anti/syn). However, the distereoselectivity when using crotyl bromide was poor and other functionalized allyl bromides under our method afforded low enantioselectivities for the alcohol products. In these types of indium-mediated additions, solvent plays a major role in determining the nature of the organoindium intermediate and we observed the susceptibility of some allylindium intermediates to hydrolysis in protic solvents. Under our reaction conditions using a polar aprotic solvent, we suggest that an allylindium(III) species is the active allylating intermediate. In addition, we have observed the presence of a shiny, indium(0) nugget throughout the reaction, irrespective of the stoichiometry, indicating disproportionation of indium halide byproduct formed during the reaction.

Halogenated solvent remediation

DOEpatents

Sorenson, Jr., Kent S.

2008-11-11

Methods for enhancing bioremediation of ground water contaminated with nonaqueous halogenated solvents are disclosed. An illustrative method includes adding an electron donor for microbe-mediated anaerobic reductive dehalogenation of the halogenated solvents, which electron donor enhances mass transfer of the halogenated solvents from residual source areas into the aqueous phase of the ground water. Illustrative electron donors include C.sub.2-C.sub.4 carboxylic acids and hydroxy acids, salts thereof, esters of C.sub.2-C.sub.4 carboxylic acids and hydroxy acids, and mixtures thereof, of which lactic acid, salts of lactic acid--such as sodium lactate, lactate esters, and mixtures thereof are particularly illustrative. The microbes are either indigenous to the ground water, or such microbes can be added to the ground water in addition to the electron donor.

Sulfamide-Lattice Restructuring To Form Dimensionally Controlled Molecular Arrays and Gel-Forming Systems.

PubMed

Raghava, Saripalli V; Gopinath, Pushparathinam; Srivastava, Bhartendu K; Ramkumar, Venkatachalam; Muraleedharan, Kannoth M

2017-03-13

A design approach that incorporates structural requirements for the formation of a 1D assembly, fibril stability, and fibril-fibril interactions for gelation was attempted by using amino acid-based sulfamides with the general structure Aa-NH-SO 2 -NH-Aa (Aa=amino acid). A preference for 1D assembly alone was not a sufficient condition for gelation, which became evident from studies involving sulfamide esters 1-5. Reducing the crystallization tendency without hindering unidirectional growth was executed through diacids of the sulfamide precursors with various amines that form an envelope around the sulfamide core through salt bridges. This strategy was fruitful, and gels of a wide variety of solvents could be formed by varying the acid and amine components. The use of dodecylamine or benzylamine, which could stabilize the molecular layers through alkyl-chain segregation or π-π interactions improved the gelation tendency, whereas the nature of the amino acid side chain, especially the rotational freedom and hydrophobicity, had a direct role in dictating the solvent preference. Crystallographic studies of these two-component systems gave molecular-level insight into the assembly and showed the importance of anisotropy in the distribution of secondary interactions in gelation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Controlling Mechanical Properties of Bis-leucine Oxalyl Amide Gels

NASA Astrophysics Data System (ADS)

Chang, William; Carvajal, Daniel; Shull, Kenneth

2011-03-01

is-leucine oxalyl amide is a low molecular weight gelator capable of gelling polar and organic solvents. A fundamental understanding of self-assembled systems can lead to new methods in drug delivery and the design of new soft material systems. An important feature of self-assembled systems are the intermolecular forces between solvent and gelator molecule; by changing the environment the gel is in, the mechanical properties also change. In this project two variables were considered: the degree of neutralization present for the gelator molecule from neutral to completely ionized, and the concentration of the gelator molecule, from 1 weight percent to 8 weight percent in 1-butanol. Mechanical properties were studied using displacement controlled indentation techniques and temperature sweep rheometry. It has been found that properties such as the storage modulus, gelation temperature and maximum stress allowed increase with bis-leucine oxalyl amide concentration. The results from this study establish a 3-d contour map between the gelator concentration, the gelator degree of ionization and mechanical properties such as storage modulus and maximum stress allowed. The intermolecular forces between the bis-leucine low molecular weight gelator and 1-butanol govern the mechanical properties of the gel system, and understanding these interactions will be key to rationally designed self-assembled systems.

Communication: Self-assembly of a model supramolecular polymer studied by replica exchange with solute tempering

NASA Astrophysics Data System (ADS)

Arefi, Hadi H.; Yamamoto, Takeshi

2017-12-01

Conventional molecular-dynamics (cMD) simulation has a well-known limitation in accessible time and length scales, and thus various enhanced sampling techniques have been proposed to alleviate the problem. In this paper, we explore the utility of replica exchange with solute tempering (REST) (i.e., a variant of Hamiltonian replica exchange methods) to simulate the self-assembly of a supramolecular polymer in explicit solvent and compare the performance with temperature-based replica exchange MD (T-REMD) as well as cMD. As a test system, we consider a relatively simple all-atom model of supramolecular polymerization (namely, benzene-1,3,5-tricarboxamides in methylcyclohexane solvent). Our results show that both REST and T-REMD are able to predict highly ordered polymer structures with helical H-bonding patterns, in contrast to cMD which completely fails to obtain such a structure for the present model. At the same time, we have also experienced some technical challenge (i.e., aggregation-dispersion transition and the resulting bottleneck for replica traversal), which is illustrated numerically. Since the computational cost of REST scales more moderately than T-REMD, we expect that REST will be useful for studying the self-assembly of larger systems in solution with enhanced rearrangement of monomers.

Space Shuttle Reusable Solid Rocket Motor (RSRM) Hand Cleaning Solvent Replacement at Kennedy Space Center (KSC)

NASA Technical Reports Server (NTRS)

Keen, Jill M.; DeWeese, Darrell C.; Key, Leigh W.

1997-01-01

At Kennedy Space Center (KSC), Thiokol Corporation provides the engineering to assemble and prepare the Space Shuttle Reusable Solid Rocket Motor (RSRM) for launch. This requires hand cleaning over 86 surfaces including metals, adhesives, rubber and electrical insulations, various painted surfaces and thermal protective materials. Due to the phase-out of certain ozone depleting chemical (ODC) solvents, all RSRM hand wipe operations being performed at KSC using l,l,1-trichloroethane (TCA) were eliminated. This presentation summarizes the approach used and the data gathered in the effort to eliminate TCA from KSC hand wipe operations.

UV-induced solvent free synthesis of truxillic acid-bile acid conjugates

NASA Astrophysics Data System (ADS)

Koivukorpi, Juha; Kolehmainen, Erkki

2009-07-01

The solvent free UV-induced [2 + 2] intermolecular cycloaddition of two molecules of 3α-cinnamic acid ester of methyl lithocholate produced in 99% yield of α- and ɛ-truxillic acid-bis(methyl lithocholate) isomers, which possess two structurally different potential binding sites. A prerequisite for this effective solid state reaction is a proper self-assembled crystal structure of the starting conjugate crystallized from acetonitrile. The crystallization of cinnamic acid ester of methyl lithocholate from acetonitrile produces two different crystalline forms (polymorphs), which is the reason for the solid state formation of two isomers of truxillic acid-bis(methyl lithocholate).

Method for making nanoporous hydrophobic coatings

DOEpatents

Fan, Hongyou; Sun, Zaicheng

2013-04-23

A simple coating method is used to form nanoporous hydrophobic films that can be used as optical coatings. The method uses evaporation-induced self-assembly of materials. The coating method starts with a homogeneous solution comprising a hydrophobic polymer and a surfactant polymer in a selective solvent. The solution is coated onto a substrate. The surfactant polymer forms micelles with the hydrophobic polymer residing in the particle core when the coating is dried. The surfactant polymer can be dissolved and selectively removed from the separated phases by washing with a polar solvent to form the nanoporous hydrophobic film.

His-Tag-Mediated Dimerization of Chemoreceptors Leads to Assembly of Functional Nanoarrays.

PubMed

Haglin, Elizabeth R; Yang, Wen; Briegel, Ariane; Thompson, Lynmarie K

2017-11-07

Transmembrane chemotaxis receptors are found in bacteria in extended hexagonal arrays stabilized by the membrane and by cytosolic binding partners, the kinase CheA and coupling protein CheW. Models of array architecture and assembly propose receptors cluster into trimers of dimers that associate with one CheA dimer and two CheW monomers to form the minimal "core unit" necessary for signal transduction. Reconstructing in vitro chemoreceptor ternary complexes that are homogeneous and functional and exhibit native architecture remains a challenge. Here we report that His-tag-mediated receptor dimerization with divalent metals is sufficient to drive assembly of nativelike functional arrays of a receptor cytoplasmic fragment. Our results indicate receptor dimerization initiates assembly and precedes formation of ternary complexes with partial kinase activity. Restoration of maximal kinase activity coincides with a shift to larger complexes, suggesting that kinase activity depends on interactions beyond the core unit. We hypothesize that achieving maximal activity requires building core units into hexagons and/or coalescing hexagons into the extended lattice. Overall, the minimally perturbing His-tag-mediated dimerization leads to assembly of chemoreceptor arrays with native architecture and thus serves as a powerful tool for studying the assembly and mechanism of this complex and other multiprotein complexes.

Enzymes from solvent-tolerant microbes: useful biocatalysts for non-aqueous enzymology.

PubMed

Gupta, Anshu; Khare, S K

2009-01-01

Solvent-tolerant microbes are a newly emerging class that possesses the unique ability to thrive in the presence of organic solvents. Their enzymes adapted to mediate cellular and metabolic processes in a solvent-rich environment and are logically stable in the presence of organic solvents. Enzyme catalysis in non-aqueous/low-water media is finding increasing applications for the synthesis of industrially important products, namely peptides, esters, and other trans-esterification products. Solvent stability, however, remains a prerequisite for employing enzymes in non-aqueous systems. Enzymes, in general, get inactivated or give very low rates of reaction in non-aqueous media. Thus, early efforts, and even some recent ones, have aimed at stabilization of enzymes in organic media by immobilization, surface modifications, mutagenesis, and protein engineering. Enzymes from solvent-tolerant microbes appear to be the choicest source for studying solvent-stable enzymes because of their unique ability to survive in the presence of a range of organic solvents. These bacteria circumvent the solvent's toxic effects by virtue of various adaptations, e.g. at the level of the cytoplasmic membrane, by degradation and transformation of solvents, and by active excretion of solvents. The recent screening of these exotic microbes has generated some naturally solvent-stable proteases, lipases, cholesterol oxidase, cholesterol esterase, cyclodextrin glucanotransferase, and other important enzymes. The unique properties of these novel biocatalysts have great potential for applications in non-aqueous enzymology for a range of industrial processes.

Effect of solvent and subsequent thermal annealing on the performance of phenylenevinylene copolymer: PCBM solar cells.

PubMed

Sharma, G D; Suresh, P; Sharma, S S; Vijay, Y K; Mikroyannidis, John A

2010-02-01

The morphology of the photoactive layer used in the bulk heterojunction photovoltaic devices is crucial for efficient charge generation and their collection at the electrodes. We investigated the solvent vapor annealing and thermal annealing effect of an alternating phenylenevinylene copolymer P:PCBM blend on its morphology and optical properties. The UV-visible absorption spectroscopy shows that both solvent and thermal annealing can result in self-assembling of copolymer P to form an ordered structure, leading to enhanced absorption in the red region and hole transport enhancement. By combining the solvent and thermal annealing of the devices, the power conversion efficiency is improved. This feature was attributed to the fact that the PCBM molecules begin to diffuse into aggregates and together with the ordered copolymer P phase form bicontinuous pathways in the entire layer for efficient charge separation and transport. Furthermore, the measured photocurrent also suggests that the space charges no longer limit the values of the short circuit current (J(sc)) and fill factor (FF) for solvent-treated and thermally annealed devices. These results indicate that the higher J(sc) and PCE for the solvent-treated and thermally annealed devices can be attributed to the phase separation of active layers, which leads to a balanced carrier mobility. The overall PCE of the device based on the combination of solvent annealing and thermal annealing is about 3.7 %.

Transient rheology of stimuli responsive hydrogels: Integrating microrheology and microfluidics

NASA Astrophysics Data System (ADS)

Sato, Jun

Stimuli-responsive hydrogels have diverse potential applications in the field of drug delivery, tissue engineering, agriculture, cosmetics, gene therapy, and as sensors and actuators due to their unique responsiveness to external signals, such as pH, temperature, and ionic strength. Understanding the responsiveness of hydrogel structure and rheology to these stimuli is essential for designing materials with desirable performance. However, no instrumentation and well-defined methodology are available to characterize the structural and rheological responses to rapid solvent changes. In this thesis, a new microrheology set-up is described, which allows us to quantitatively measure the transient rheological properties and microstructure of a variety of solvent-responsive complex fluids. The device was constructed by integrating particle tracking microrheology and microfluidics and offers unique experimental capabilities for performing solvent-reponse measurements on soft fragile materials without applying external shear forces. Transient analysis methods to quantitatively obtain rheological properties were also constructed, and guidelines for the trade-off between statistical validity and temporal resolution were developed to accurately capture physical transitions. Employing the new device and methodology, we successfully quantified the transient rheological and microstructural responses during gel formation and break-up, and viscosity changes of solvent-responsive complex fluids. The analysis method was expanded for heterogeneous samples, incorporating methods to quantify the microrheology of samples with broad distributions of individual particle dynamics. Transient microrheology measurements of fragile, heterogeneous, self-assembled block copolypeptide hydrogels revealed that solvent exchange via convective mixing and dialysis can lead to significantly different gel properties and that commonly applied sample preparation protocols for the characterization of soft biomaterials could lead to erroneous conclusions about microstructural dynamics. Systematic investigations by varying key parameters, like molecular structure, gel concentration, salt concentration, and tracer particle size for microrheology, revealed that subtle variations in molecular architecture can cause major changes in response dynamics. Moreover, the results showed that the method can be applied for studying gel formation and breakup kinetics. The research in this thesis facilitates the design of solvent-responsive soft materials with appropriate microstructural dynamics for in vivo applications like tissue engineering and drug delivery, and can also be applied to study the effect of solvents on self-assembly mechanisms in other responsive soft materials, such as polymer solutions and colloidal dispersions.

The solvent-gelator interaction as the origin of different diffusivity behavior of diols in gels formed with sugar-based low-molecular-mass gelator.

PubMed

Kowalczuk, Joanna; Bielejewski, Michał; Lapiński, Andrzej; Luboradzki, Roman; Tritt-Goc, Jadwiga

2014-04-10

Organogels are soft materials consisting of low-molecular-mass gelators (LMOGs) self-assembled through noncovalent interactions into 3D structures, in which free spaces are filled by organic solvents. 4,6,4',6'-O-terephthylidene-bis(methyl-α-d-glucopyranoside) (1) is found to be a new LMOG. It gelatinizes only a limited number of solvents. Here, the gels of 1 with ethylene glycol (EG) and 1,3-propanediol (PG) are investigated with FT-IR, Raman, and UV-vis spectroscopies, the NMR relaxometry and diffusometry methods, and microscopic observation. The chemical structures of both solvents are closely related, but the variety of physical characteristics of the gels is large. The 1/PG gels are thermally more stable compared to 1/EG gels. The types of aggregates are most likely the H- and J-type in 1/EG gels and the J-type in 1/PG gels. Different microstructures are observed: bundles of crossing fibers for 1/EG and a honeycomb-like matrix for 1/PG gels. The diffusivity of the EG solvent in gels with 1 behaves as expected, decreasing with increasing gelator concentration, whereas the opposite behavior is observed for the PG solvent. This is a most fascinating result. To explain the diffusion enhancement, we suggest that a dynamic hydrogen bonding network of PG solvent in gel matrixes is disrupted due to solvent-gelator interaction. The direct proof of this interaction is given by the observed low frequency dispersion of the spin-lattice relaxation time of solvents in the gel matrixes.

Following in Real Time the Two-Step Assembly of Nanoparticles into Mesocrystals in Levitating Drops.

PubMed

Agthe, Michael; Plivelic, Tomás S; Labrador, Ana; Bergström, Lennart; Salazar-Alvarez, German

2016-11-09

Mesocrystals composed of crystallographically aligned nanocrystals are present in biominerals and assembled materials which show strongly directional properties of importance for mechanical protection and functional devices. Mesocrystals are commonly formed by complex biomineralization processes and can also be generated by assembly of anisotropic nanocrystals. Here, we follow the evaporation-induced assembly of maghemite nanocubes into mesocrystals in real time in levitating drops. Analysis of time-resolved small-angle X-ray scattering data and ex situ scanning electron microscopy together with interparticle potential calculations show that the substrate-free, particle-mediated crystallization process proceeds in two stages involving the formation and rapid transformation of a dense, structurally disordered phase into ordered mesocrystals. Controlling and tailoring the particle-mediated formation of mesocrystals could be utilized to assemble designed nanoparticles into new materials with unique functions.

Direct and Quantitative Characterization of Dynamic Ligand Exchange between Coordination-Driven Self-Assembled Supramolecular Polygons

PubMed Central

Zheng, Yao-Rong; Stang, Peter J.

2009-01-01

The direct observation of dynamic ligand exchange beween Pt-N coordination-driven self-assembled supramolecular polygons (triangles and rectangles) has been achieved using stable isotope labeling (1H/2D) of the pyridyl donors and electrospray ionization mass spectrometry (ESI-MS) together with NMR spectroscopy. Both the thermodynamic and kinetic aspects of such exchange processes have been established based on quantitative mass spectral results. Further investigation showed that the exchange is highly dependent on experimental conditions such as temperature, solvent, and the counter anions. PMID:19243144

Direct and quantitative characterization of dynamic ligand exchange between coordination-driven self-assembled supramolecular polygons.

PubMed

Zheng, Yao-Rong; Stang, Peter J

2009-03-18

The direct observation of dynamic ligand exchange between Pt-N coordination-driven self-assembled supramolecular polygons (triangles and rectangles) has been achieved using stable (1)H/(2)D isotope labeling of the pyridyl donors and electrospray ionization mass spectrometry combined with NMR spectroscopy. Both the thermodynamic and kinetic aspects of such exchange processes have been established on the basis of quantitative mass spectral results. Further investigation has shown that the exchange is highly dependent on experimental conditions such as temperature, solvent, and the counteranions.

Linifanib--a multi-targeted receptor tyrosine kinase inhibitor and a low molecular weight gelator.

PubMed

Marlow, Maria; Al-Ameedee, Mohammed; Smith, Thomas; Wheeler, Simon; Stocks, Michael J

2015-04-14

In this study we demonstrate that linifanib, a multi-targeted receptor tyrosine kinase inhibitor, with a key urea containing pharmacophore, self-assembles into a hydrogel in the presence of low amounts of solvent. We demonstrate the role of the urea functional group and that of fluorine substitution on the adjacent aromatic ring in promoting self-assembly. We have also shown that linifanib has superior mechanical strength to two structurally related analogues and hence increased potential for localisation at an injection site for drug delivery applications.

Controlling the Pore Size of Mesoporous Carbon Thin Films through Thermal and Solvent Annealing.

PubMed

Zhou, Zhengping; Liu, Guoliang

2017-04-01

Herein an approach to controlling the pore size of mesoporous carbon thin films from metal-free polyacrylonitrile-containing block copolymers is described. A high-molecular-weight poly(acrylonitrile-block-methyl methacrylate) (PAN-b-PMMA) is synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The authors systematically investigate the self-assembly behavior of PAN-b-PMMA thin films during thermal and solvent annealing, as well as the pore size of mesoporous carbon thin films after pyrolysis. The as-spin-coated PAN-b-PMMA is microphase-separated into uniformly spaced globular nanostructures, and these globular nanostructures evolve into various morphologies after thermal or solvent annealing. Surprisingly, through thermal annealing and subsequent pyrolysis of PAN-b-PMMA into mesoporous carbon thin films, the pore size and center-to-center spacing increase significantly with thermal annealing temperature, different from most block copolymers. In addition, the choice of solvent in solvent annealing strongly influences the block copolymer nanostructure and the pore size of mesoporous carbon thin films. The discoveries herein provide a simple strategy to control the pore size of mesoporous carbon thin films by tuning thermal or solvent annealing conditions, instead of synthesizing a series of block copolymers of various molecular weights and compositions. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Three-dimensional block copolymer nanostructures by the solvent-annealing-induced wetting in anodic aluminum oxide templates.

PubMed

Chu, Chiang-Jui; Chung, Pei-Yun; Chi, Mu-Huan; Kao, Yi-Huei; Chen, Jiun-Tai

2014-09-01

Block copolymers have been extensively studied over the last few decades because they can self-assemble into well-ordered nanoscale structures. The morphologies of block copolymers in confined geometries, however, are still not fully understood. In this work, the fabrication and morphologies of three-dimensional polystyrene-block-polydimethylsiloxane (PS-b-PDMS) nanostructures confined in the nanopores of anodic aluminum oxide (AAO) templates are studied. It is discovered that the block copolymers can wet the nanopores using a novel solvent-annealing-induced nanowetting in templates (SAINT) method. The unique advantage of this method is that the problem of thermal degradation can be avoided. In addition, the morphologies of PS-b-PDMS nanostructures can be controlled by changing the wetting conditions. Different solvents are used as the annealing solvent, including toluene, hexane, and a co-solvent of toluene and hexane. When the block copolymer wets the nanopores in toluene vapors, a perpendicular morphology is observed. When the block copolymer wets the nanopores in co-solvent vapors (toluene/hexane = 3:2), unusual circular and helical morphologies are obtained. These three-dimensional nanostructures can serve as naontemplates for refilling with other functional materials, such as Au, Ag, ZnO, and TiO2 . © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Surfaces wettability and morphology modulation in a fluorene derivative self-assembly system

NASA Astrophysics Data System (ADS)

Cao, Xinhua; Gao, Aiping; Zhao, Na; Yuan, Fangyuan; Liu, Chenxi; Li, Ruru

2016-04-01

A new organogelator based on fluorene derivative (gelator 1) was designed and synthesized. Organogels could be obtained via the self-assembly of the derivative in acetone, toluene, ethyl acetate, hexane, DMSO and petroleum ether. The self-assembly process was thoroughly characterized using field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), UV-vis, FT-IR and the contact angle. Surfaces with different morphologies and wetting properties were formed via the self-assembly of gelator 1 in the six different solvents. Interestingly, a superhydrophobic surface with a contact angle of 150° was obtained from organogel 1 in DMSO and exhibited the lotus-effect. The sliding angle necessary for a water droplet to move on the glass was only 15°. Hydrogen bonding and van der Waals forces were attributed as the main driving forces for gel formation.

Process for preparing an assembly of an article and a polyimide which resists dimensional change, delamination and debonding when exposed to changes in temperature

NASA Technical Reports Server (NTRS)

Stoakley, Diane M. (Inventor); St.clair, Anne K. (Inventor)

1994-01-01

An assembly of an article and a polyimide composition is prepared. The assembly resists dimensional change, delamination, or debonding when exposed to changes in temperature. An article is provided. A polyamic acid solution which yields a polyimide having a low coefficient of thermal expansion (CTE) was prepared. Equimolar quantities of an aromatic diamine and an aromatic dianhydride were reacted in a solvent medium to form a polyamic acid solution. A metal ion-containing additive was added to the solution. Examples of this additive are: TbCl3, DyCl3, ErCl3, TmCl3, Al(C5H7O2)3, and Er2S3. The polyamic acid solution was imidized and is combined with the article to form the assembly.

A Convenient, TiCl4/SnCl4-Mediated Synthesis of N-Phenyl or N-Aryl Benzamidines and N-Phenylpicolinamidines

PubMed Central

Patil, Umesh D.; Mahulikar, Pramod P.

2012-01-01

A new, TiCl4-or SnCl4-mediated, solvent-free method was developed for the synthesis of N-Aryl benzamidines and N-phenylpicolinamidines, in moderate-to-good yield, using suitable amines and nitriles as starting materials. PMID:24052858

Homopolymer self-assembly into stable nanoparticles: concerted action of hydrophobic association and hydrogen bonding in thermoresponsive poly(alkylacrylic acid)s.

PubMed

Sedlák, Marián

2012-03-01

A new approach to polymer self-assembly was presented recently [M. Sedlák, Č. Koňák, J. Dybal, Macromolecules 2009, 2, 7430-7438 and 7439-7446.] (1, 2) where stable polymeric nanoparticles were formed from poly(ethylacrylic acid) homopolymers without any assembly triggering additives, simply by heating polymer solution under conditions of thermosensitivity to certain temperature. In the current Article, we present successful results on poly(propylacrylic acid), which is a more hydrophobic polymer. We also present results on a less hydrophobic polymer from this series, poly(methacrylic acid), from which nanoparticles cannot be formed. Comparison of results on all three polymers gives a solid physicochemical insight and supports the molecular mechanism of the self-assembly previously suggested: The solvent quality gradually worsens upon heating of a thermosensitive polymer solution, and polymer-polymer contacts are preferred over polymer-solvent contacts, which leads to the formation of polymer assemblies. The presence of a significant amount of charge on chains prevents macroscopic phase separation. Upon subsequent cooling to laboratory temperature, the assemblies (nanoparticles) should eventually dissolve; however, this is not the case due to the fact that polymer chains brought to a close proximity at elevated temperatures become hydrogen-bonded. In addition, hydrogen bonds strengthen upon cooling. Mainly carboxylic-carboxylate hydrogen bonds (COOH····COO(-)) are responsible for the irreversibility of the process and the stability of nanoparticles. Conclusions are supported by results from static and dynamic light scattering, FTIR spectroscopy, and cryo-TEM microscopy. Size of nanoparticles can be monitored during the growth and custom-tailored by tuning critical parameters, especially the degree of ionization, temperature, and time of heating. Nanoparticles are stable over long periods of time. They are stable in a broad range of salt concentrations, including physiological conditions, and possess a mild acceptable degree of polydispersity.

Using Denatured Egg White as a Macroscopic Model for Teaching Protein Structure and Introducing Protein Synthesis for High School Students

NASA Astrophysics Data System (ADS)

Correia, Paulo R. M.; Torres, Bayardo B.

2007-12-01

The success of teaching molecular and atomic phenomena depends on the didactical strategy and the media selection adopted, in consideration of the level of abstraction of the subject to be taught and the students' capability to deal with abstract operations. Dale's cone of experience was employed to plan three 50-minute classes to discuss protein denaturation from a chemical point of view. Only low abstraction level activities were selected: (i) two demonstrations showing the denaturation of albumin by heating and by changing the solvent, (ii) the assembly of a macroscopic model representing the protein molecule, and (iii) a role-play for simulating glucagon synthesis. A student-centered approach and collaborative learning were used throughout the classes. The use of macroscopic models is a powerful didactical strategy to represent molecular and atomic events. They can convert microscopic entities into touchable objects, reducing the abstraction level required to discuss chemistry with high school students. Thus, interesting topics involving molecules and their behavior can take place efficiently when mediated by concrete experiences.

Polyelectrolyte-Surfactant Complexes: A New Class of Organogelators

NASA Astrophysics Data System (ADS)

Cavicchi, Kevin; Liu, Yuqing; Guzman, Gustavo

2011-03-01

Polyelectrolyte-surfactant complexes (PE-SURFs) are a class of polymers generated by neutralizing a polyelectrolyte with an oppositely charged surfactant. It has been found that PE-SURFs composed of polystyrene sulfonate and long chain alkyl dimethyl amines act as good organogelators for a range of hydrophobic, organic solvents. Thermo-reversible organogels are formed by heating and cooling PE-SURF/solvent solutions. The gel transition temperature is influenced by the degree of polymerization, the length of the alkyl side-chain, the solubility parameter of the solvent, and the concentration of the gelator. Freeze-drying and scanning electron microscopy characterization of the resultant xerogels shows the formation of rod- and plate-like network morphologies depending on the system parameters. This behavior is consistent with gelation driven by the self-assembly of the amphiphilic PE-SURFs into micellar networks.

Gels and lyotropic liquid crystals: using an imidazolium-based catanionic surfactant in binary solvents.

PubMed

Cheng, Ni; Hu, Qiongzheng; Bi, Yanhui; Xu, Wenwen; Gong, Yanjun; Yu, Li

2014-08-05

The self-assembly behavior of an imidazolium-based catanionic surfactant, 1-butyl-3-methylimidazolium dodecylsulfate ([C4mim][C12H25SO4]), was investigated in water-ethylammonium nitrate (EAN) mixed solvents with different volume ratios. It is particular interesting that this simple surfactant could not only form lyotropic liquid crystals (LLC) with multimesophases, i.e., normal hexagonal (H1), lamellar liquid crystal (Lα), and reverse bicontinuous cubic phase (V2), in the water-rich environment but also act as an efficient low-molecular-weight gelator (LMWG) which gelated EAN-abundant binary media in a broad concentration range. The peculiar nanodisk cluster morphology of gels composed of similar bilayer units was first observed. FT-IR spectra and density functional theory (DFT) calculations reveal that strong H bonding and electrostatic interactions between EAN and the headgroups of [C4mim][C12H25SO4] are primarily responsible for gelation. The self-assembled gels displayed excellent mechanical strength and a thermoreversible sol-gel transition. It is for the first time that a rich variety of controllable ordered aggregates could be observed only by simply modulating the concentration of a single imidazolium-based catanionic surfactant or the ratio of mixed solvents. This environmentally friendly system is expected to have broad applications in various fields, such as materials science, drug delivery systems, and supramolecular chemistry.

Curvature-Mediated Assembly of Janus Nanoparticles on Membrane Vesicles.

PubMed

Bahrami, Amir Houshang; Weikl, Thomas R

2018-02-14

Besides direct particle-particle interactions, nanoparticles adsorbed to biomembranes experience indirect interactions that are mediated by the membrane curvature arising from particle adsorption. In this Letter, we show that the curvature-mediated interactions of adsorbed Janus particles depend on the initial curvature of the membrane prior to adsorption, that is, on whether the membrane initially bulges toward or away from the particles in our simulations. The curvature-mediated interaction can be strongly attractive for Janus particles adsorbed to the outside of a membrane vesicle, which initially bulges away from the particles. For Janus particles adsorbed to the vesicle inside, in contrast, the curvature-mediated interactions are repulsive. We find that the area fraction of the adhesive Janus particle surface is an important control parameter for the curvature-mediated interaction and assembly of the particles, besides the initial membrane curvature.

Protein S is inducible by interleukin 4 in T cells and inhibits lymphoid cell procoagulant activity

PubMed Central

Smiley, Stephen T.; Boyer, Sarah N.; Heeb, Mary J.; Griffin, John H.; Grusby, Michael J.

1997-01-01

Extravascular procoagulant activity often accompanies cell-mediated immune responses and systemic administration of pharmacologic anticoagulants prevents cell-mediated delayed-type hypersensitivity reactions. These observations suggest a direct association between coagulation and cell-mediated immunity. The cytokine interleukin (IL)-4 potently suppresses cell-mediated immune responses, but its mechanism of action remains to be determined. Herein we demonstrate that the physiologic anticoagulant protein S is IL-4-inducible in primary T cells. Although protein S was known to inhibit the classic factor Va-dependent prothrombinase assembled by endothelial cells and platelets, we found that protein S also inhibits the factor Va-independent prothrombinase assembled by lymphoid cells. Thus, protein S-mediated down-regulation of lymphoid cell procoagulant activity may be one mechanism by which IL-4 antagonizes cell-mediated immunity. PMID:9326636

Molecular lego for the assembly of biosensing layers.

PubMed

Mano, N; Kuhn, A

2005-03-31

We propose a procedure to assemble monolayers of redox mediator, coenzyme, enzyme and stabilizing polyelectrolyte on an electrode surface using essentially electrostatic and complexing interactions. In a first step a monolayer of redox mediator, substituted nitrofluorenones, is adsorbed. In a second step, a layer of calcium cations is immobilized at the interface. It establishes a bridge between the redox mediator and the subsequently adsorbed coenzyme NAD(+). In the next step we use the intrinsic affinity of the NAD(+) monolayer for dehydrogenases to build up a multilayer composed of mediator/Ca(2+)/NAD(+)/dehydrogenase. The so obtained modified electrode can be used as a biosensor. Quartz crystal microbalance measurements allowed us to better understand the different parameters responsible for the adsorption. A more detailed investigation of the system made it possible to finally stabilize the assembly sufficiently by the adsorption of a polyelectrolyte layer in order to perform rotating disk electrode measurements with the whole supramolecular architecture on the electrode surface.

75 FR 52309 - Notice of Petitions by Firms for Determination of Eligibility To Apply for Trade Adjustment...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-08-25

... manufactures parts and assemblies. Bracalente Manufacturing Company, Inc. 20 W. Creamery Road, 8/2/2010 The.... electrical wiring harnesses and lighting fixture components whose primary manufacturing material is copper... and Mill, SC 29715. coatings whose manufacturing materials include pigments, resins, solvents...

Development and Modeling of a Novel Self-Assembly Process for Polymer and Polymeric Composite Nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sumpter, Bobby G.; Carrillo, Jan-Michael Y.; Ahn, Suk-Kyun

Extensive computational simulations and experiments have been used to investigate the structure, dynamics and resulting photophysical properties of a number para-phenylenevinylene (PPV) based polymers and oligomers. These studies have shown how the morphology and structure are controlled to a large extent by the nature of the solute-solvent interactions in the initial solution phase preparation. A good solvent such as dichloromethane generates non-compact structures with more of a defect-extended chain like morphology while a bad solvent such as toluene leads to compact organized and folded structures with rod-like morphologies. Secondary structural organization is induced by using the solution phase structures tomore » generate solvent-free single molecule nanoparticles. These nanoparticles are very compact and rod shaped, consisting of near-cofacial ordering of the conjugated PPV chain backbones between folds located at tetrahedral defects (sp3 C-C bonds). The resulting photophysical properties exhibit a significant enhancement in the photoluminescence quantum yield, lifetime, and stability. In addition, the single molecule nanoparticles have Gaussian-like emission spectra with discrete center frequencies that are correlated to a conjugation length, allowing the design of nanoparticles which luminesces at a particular frequency. We followed a similar approach and applied a comparable methodology in our recent work on polythiophenes in order to study the effect of polymer architecture on nanoscale assembly. Unlike linear chains of comparable size, we observed aggregation of the bottlebrush architecture of poly(norbornene)-g-poly(3-hexylthiophene) (PNB-g-P3HT) after the freeze-drying and dissolution processes. The behavior can be attributed to a significant enhancement in the number of π-π interactions between grafted P3HT side chains.« less

Development of Self-Assembled Nanoscale Templates via Microphase Separation Induced by Polymer Brushes

NASA Astrophysics Data System (ADS)

Chu, Elza

Phase separation in soft matter has been the crucial element in generating hybrid materials, such as polymer blends and mixed polymer brushes. This dissertation discusses two methods of developing self-assembled nanoscale templates via microphase separation induced by polymer brush synthesis. This work introduces a novel soft substrate approach with renewable grafting sites where polyacrylamide is "grafted through" chitosan soft substrates. The mechanism of grafting leads to ordered arrays of filament-like nanostructures spanning the chitosan-air interface. Additionally, the chemical composition of the filaments allows for post-chemical modification to change the physical properties of the filaments, and subsequently tailor surfaces for specific application. Unlike traditional materials, multi-functional or "smart" materials, such as binary polymer brushes (BPB) are capable of spontaneously changing the spatial distribution of functional groups and morphology at the surface upon external stimuli. Although promising in principle, the limited range of available complementary polymers with common non-selective solvents confines the diversity of usable materials and restricts any further advancement in the field. This dissertation also covers the fabrication and characterization of responsive nanoscale polystyrene templates or "mosaic" brushes that are capable of changing interfacial composition upon exposure to varying solvent qualities. Using a "mosaic" brush template is a unique approach that allows the fabrication of strongly immiscible polymer BPB without the need for a common solvent. The synthesis of such BPB is exemplified by two strongly immiscible polymers, i.e. polystyrene (polar) and polyacrylamide (non-polar), where polyacrylamide brush is "graft through" a Si-substrate modified with the polystyrene collapsed "mosaic" brush. The surface exhibits solvent-triggered responses, as well as application potential for anti-biofouling.

Tuning carbon nanotube assembly for flexible, strong and conductive films

NASA Astrophysics Data System (ADS)

Wang, Yanjie; Li, Min; Gu, Yizhuo; Zhang, Xiaohua; Wang, Shaokai; Li, Qingwen; Zhang, Zuoguang

2015-02-01

Carbon nanotubes are ideal scaffolds for designing and architecting flexible graphite films with tunable mechanical, electrical and thermal properties. Herein, we demonstrate that the assembly of aligned carbon nanotubes with different aggregation density and morphology leads to different mechanical properties and anisotropic electrical conduction along the films. Using drying evaporation under tension treatment, the carbon nanotubes can be assembled into strong films with tensile strength and Young's modulus as high as 3.2 GPa and 124 GPa, respectively, leading to a remarkable toughness of 54.38 J g-1, greatly outperforming conventional graphite films, spider webs and even Kevlar fiber films. Different types of solvents may result in the assembly of CNTs with different aggregation morphology and therefore different modulus. In addition, we reveal that the high density assembly of aligned CNTs correlates with better electric conduction along the axial direction, enabling these flexible graphite films to be both strong and conductive.Carbon nanotubes are ideal scaffolds for designing and architecting flexible graphite films with tunable mechanical, electrical and thermal properties. Herein, we demonstrate that the assembly of aligned carbon nanotubes with different aggregation density and morphology leads to different mechanical properties and anisotropic electrical conduction along the films. Using drying evaporation under tension treatment, the carbon nanotubes can be assembled into strong films with tensile strength and Young's modulus as high as 3.2 GPa and 124 GPa, respectively, leading to a remarkable toughness of 54.38 J g-1, greatly outperforming conventional graphite films, spider webs and even Kevlar fiber films. Different types of solvents may result in the assembly of CNTs with different aggregation morphology and therefore different modulus. In addition, we reveal that the high density assembly of aligned CNTs correlates with better electric conduction along the axial direction, enabling these flexible graphite films to be both strong and conductive. Electronic supplementary information (ESI) available: The TEM image of array CNTs. The surface height curves of x-z cross-section of the films. A comparison of the mechanical properties of the pure CNT films described in this work with other CNT films/fibers spun from CNT array reported in the literature. The measured evaporation rates of ethanol and acetone. See DOI: 10.1039/c4nr06401a

Computational screening of biomolecular adsorption and self-assembly on nanoscale surfaces.

PubMed

Heinz, Hendrik

2010-05-01

The quantification of binding properties of ions, surfactants, biopolymers, and other macromolecules to nanometer-scale surfaces is often difficult experimentally and a recurring challenge in molecular simulation. A simple and computationally efficient method is introduced to compute quantitatively the energy of adsorption of solute molecules on a given surface. Highly accurate summation of Coulomb energies as well as precise control of temperature and pressure is required to extract the small energy differences in complex environments characterized by a large total energy. The method involves the simulation of four systems, the surface-solute-solvent system, the solute-solvent system, the solvent system, and the surface-solvent system under consideration of equal molecular volumes of each component under NVT conditions using standard molecular dynamics or Monte Carlo algorithms. Particularly in chemically detailed systems including thousands of explicit solvent molecules and specific concentrations of ions and organic solutes, the method takes into account the effect of complex nonbond interactions and rotational isomeric states on the adsorption behavior on surfaces. As a numerical example, the adsorption of a dodecapeptide on the Au {111} and mica {001} surfaces is described in aqueous solution. Copyright 2009 Wiley Periodicals, Inc.

An in situ grazing incidence x-ray scattering study of block copolymer thin films during solvent vapor annealing

NASA Astrophysics Data System (ADS)

Gu, Xiaodan; Gunkel, Ilja; Hexemer, Alexander; Russell, Thomas

2014-03-01

Although solvent vapor annealing (SVA) has been widely applied to block copolymer (BCP) thin films to obtain well-ordered microdomains, the mechanism of enhancing lateral order is not well understood. Here, we used real time in situ grazing-incidence small-angle x-ray scattering (in situGISAXS) to study the self-assembly of PS-b-P2VP BCP BCPs with different molecular weights thin films in THF vapor, a near neutral solvent for both blocks. Both swelling and deswelling behavior of BCP thin films were examined. The extent of swellingand the solvent removal rate not only affect the domain spacing of BCPs but also dictate the extent of lateral ordering of the BCP microdomains. Larger grains were observed at higher values of the swelling ratio (close to disordering). To preserve the maximal lateral ordering of the microdomains in the swollen state, the fastest solvent removal rate is required to freeze in the ordered microdomain structure of the swollen BCP film. We thanks support from U.S. Department of Energy BES under contract BES-DE-FG02-96ER45612 and ALS doctoral fellowship.

Solvent-free thermoplastic-poly(dimethylsiloxane) bonding mediated by UV irradiation followed by gas-phase chemical deposition of an adhesion linker

NASA Astrophysics Data System (ADS)

Ahn, S. Y.; Lee, N. Y.

2015-07-01

Here, we introduce a solvent-free strategy for bonding various thermoplastic substrates with poly(dimethylsiloxane) (PDMS) using ultraviolet (UV) irradiation followed by the gas-phase chemical deposition of aminosilane on the UV-irradiated thermoplastic substrates. The thermoplastic substrates were first irradiated with UV for surface hydrophilic treatment and were then grafted with vacuum-evaporated aminosilane, where the alkoxysilane side reacted with the oxidized surface of the thermoplastic substrate. Next, the amine-terminated thermoplastic substrates were treated with corona discharge to oxidize the surface and were bonded with PDMS, which was also oxidized via corona discharge. The two substrates were then hermetically sealed and pressed under atmospheric pressure for 30 min at 60 °C. This process enabled the formation of a robust siloxane bond (Si-O-Si) between the thermoplastic substrate and PDMS under relatively mild conditions using an inexpensive and commercially available UV lamp and Tesla coil. Various thermoplastic substrates were examined for bonding with PDMS, including poly(methylmethacrylate) (PMMA), polycarbonate (PC), poly(ethyleneterephthalate) (PET) and polystyrene (PS). Surface characterizations were performed by measuring the contact angle and performing x-ray photoelectron spectroscopy analysis, and the bond strength was analyzed by conducting various mechanical force measurements such as pull, delamination, leak and burst tests. The average bond strengths for the PMMA-PDMS, PC-PDMS, PET-PDMS and PS-PDMS assemblies were measured at 823.6, 379.3, 291.2 and 229.0 kPa, respectively, confirming the highly reliable performance of the introduced bonding strategy.

Huntingtin-interacting protein 1 (Hip1) and Hip1-related protein (Hip1R) bind the conserved sequence of clathrin light chains and thereby influence clathrin assembly in vitro and actin distribution in vivo.

PubMed

Chen, Chih-Ying; Brodsky, Frances M

2005-02-18

Clathrin heavy and light chains form triskelia, which assemble into polyhedral coats of membrane vesicles that mediate transport for endocytosis and organelle biogenesis. Light chain subunits regulate clathrin assembly in vitro by suppressing spontaneous self-assembly of the heavy chains. The residues that play this regulatory role are at the N terminus of a conserved 22-amino acid sequence that is shared by all vertebrate light chains. Here we show that these regulatory residues and others in the conserved sequence mediate light chain interaction with Hip1 and Hip1R. These related proteins were previously found to be enriched in clathrin-coated vesicles and to promote clathrin assembly in vitro. We demonstrate Hip1R binding preference for light chains associated with clathrin heavy chain and show that Hip1R stimulation of clathrin assembly in vitro is blocked by mutations in the conserved sequence of light chains that abolish interaction with Hip1 and Hip1R. In vivo overexpression of a fragment of clathrin light chain comprising the Hip1R-binding region affected cellular actin distribution. Together these results suggest that the roles of Hip1 and Hip1R in affecting clathrin assembly and actin distribution are mediated by their interaction with the conserved sequence of clathrin light chains.

Coordinate regulation of estrogen-mediated fibronectin matrix assembly and epidermal growth factor receptor transactivation by the G protein-coupled receptor, GPR30.

PubMed

Quinn, Jeffrey A; Graeber, C Thomas; Frackelton, A Raymond; Kim, Minsoo; Schwarzbauer, Jean E; Filardo, Edward J

2009-07-01

Estrogen promotes changes in cytoskeletal architecture not easily attributed to the biological action of estrogen receptors, ERalpha and ERbeta. The Gs protein-coupled transmembrane receptor, GPR30, is linked to specific estrogen binding and rapid estrogen-mediated release of heparin-bound epidermal growth factor. Using marker rescue and dominant interfering mutant strategies, we show that estrogen action via GPR30 promotes fibronectin (FN) matrix assembly by human breast cancer cells. Stimulation with 17beta-estradiol or the ER antagonist, ICI 182, 780, results in the recruitment of FN-engaged integrin alpha5beta1 conformers to fibrillar adhesions and the synthesis of FN fibrils. Concurrent with this cellular response, GPR30 promotes the formation of Src-dependent, Shc-integrin alpha5beta1 complexes. Function-blocking antibodies directed against integrin alpha5beta1 or soluble Arg-Gly-Asp peptide fragments derived from FN specifically inhibited GPR30-mediated epidermal growth factor receptor transactivation. Estrogen-mediated FN matrix assembly and epidermal growth factor receptor transactivation were similarly disrupted in integrin beta1-deficient GE11 cells, whereas reintroduction of integrin beta1 into GE11 cells restored these responses. Mutant Shc (317Y/F) blocked GPR30-induced FN matrix assembly and tyrosyl phosphorylation of erbB1. Interestingly, relative to recombinant wild-type Shc, 317Y/F Shc was more readily retained in GPR30-induced integrin alpha5beta1 complexes, yet this mutant did not prevent endogenous Shc-integrin alpha5beta1 complex formation. Our results suggest that GPR30 coordinates estrogen-mediated FN matrix assembly and growth factor release in human breast cancer cells via a Shc-dependent signaling mechanism that activates integrin alpha5beta1.

Supramolecular Disassembly of Facially Amphiphilic Dendrimer Assemblies in Response to Physical, Chemical, and Biological Stimuli

PubMed Central

2015-01-01

Conspectus Supramolecular assemblies formed from spontaneous self-assembly of amphiphilic macromolecules are explored as biomimetic architectures and for applications in areas such as sensing, drug delivery, and diagnostics. Macromolecular assemblies are usually preferred, compared with their simpler small molecule counterparts, due to their low critical aggregate concentrations (CAC) and high thermodynamic stability. This Account focuses on the structural and functional aspects of assemblies formed from dendrimers, specifically facially amphiphilic dendrons that form micelle or inverse micelle type supramolecular assemblies depending on the nature of the solvent medium. The micelle type assemblies formed from facially amphiphilic dendrons sequester hydrophobic guest molecules in their interiors. The stability of these assemblies is dependent on the relative compatibility of the hydrophilic and hydrophobic functionalities with water, often referred to as hydrophilic–lipophilic balance (HLB). Disruption of the HLB, using an external stimulus, could lead to disassembly of the aggregates, which can then be utilized to cause an actuation event, such as guest molecule release. Studying these possibilities has led to (i) a robust and general strategy for stimulus-induced disassembly and molecular release and (ii) the introduction of a new approach to protein-responsive supramolecular disassembly. The latter strategy provides a particularly novel avenue for impacting biomedical applications. Most of the stimuli-sensitive supramolecular assemblies have been designed to be responsive to factors such pH, temperature, and redox conditions. The reason for this interest stems from the fact that certain disease microenvironments have aberrations in these factors. However, these variations are the secondary imbalances in biology. Imbalances in protein activity are the primary reasons for most, if not all, human pathology. There have been no robust strategies in stimulus-responsive assemblies that respond to these variations. The facially amphiphilic dendrimers provide a unique opportunity to explore this possibility. Similarly, the propensity of these molecules to form inverse micelles in apolar solvents and thus bind polar guest molecules, combined with the fact that these assemblies do not thermodynamically equilibrate in biphasic mixtures, was used to predictably simplify peptide mixtures. The structure–property relationships developed from these studies have led to a selective and highly sensitive detection of peptides in complex mixtures. Selectivity in peptide extraction was achieved using charge complementarity between the peptides and the hydrophilic components present in inverse micellar interiors. These findings will have implications in areas such as proteomics and biomarker detection. PMID:24937682

Hyper-Assembly of Self-Assembled Glycoclusters Mediated by Specific Carbohydrate-Carbohydrate Interactions.

PubMed

Yan, Gengwei; Yamaguchi, Takumi; Suzuki, Tatsuya; Yanaka, Saeko; Sato, Sota; Fujita, Makoto; Kato, Koichi

2017-05-04

Hybridization of a self-assembled, spherical complex with oligosaccharides containing Lewis X, a functional trisaccharide displayed on various cell surfaces, yielded well-defined glycoclusters. The self-assembled glycoclusters exhibited homophilic hyper-assembly in aqueous solution in a Ca 2+ -dependent manner through specific carbohydrate-carbohydrate interactions, offering a structural scaffold for functional biomimetic systems. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

RISC assembly: Coordination between small RNAs and Argonaute proteins.

PubMed

Kobayashi, Hotaka; Tomari, Yukihide

2016-01-01

Non-coding RNAs generally form ribonucleoprotein (RNP) complexes with their partner proteins to exert their functions. Small RNAs, including microRNAs, small interfering RNAs, and PIWI-interacting RNAs, assemble with Argonaute (Ago) family proteins into the effector complex called RNA-induced silencing complex (RISC), which mediates sequence-specific target gene silencing. RISC assembly is not a simple binding between a small RNA and Ago; rather, it follows an ordered multi-step pathway that requires specific accessory factors. Some steps of RISC assembly and RISC-mediated gene silencing are dependent on or facilitated by particular intracellular platforms, suggesting their spatial regulation. In this review, we summarize the currently known mechanisms for RISC assembly of each small RNA class and propose a revised model for the role of the chaperone machinery in the duplex-initiated RISC assembly pathway. This article is part of a Special Issue entitled: Clues to long noncoding RNA taxonomy1, edited by Dr. Tetsuro Hirose and Dr. Shinichi Nakagawa. Copyright © 2015 Elsevier B.V. All rights reserved.

Inhibition of U snRNP assembly by a virus-encoded proteinase.

PubMed

Almstead, Laura L; Sarnow, Peter

2007-05-01

It has been proposed that defects in the assembly of spliceosomal uridine-rich small nuclear ribonucleoprotein (U snRNP) complexes could account for the death of motor neurons in spinal muscular atrophy (SMA). We discovered that infection of cultured cells with poliovirus results in the specific cleavage of the host factor Gemin3 by a virus-encoded proteinase, 2A(pro). Gemin3 is a component of the macromolecular SMN complex that mediates assembly of U snRNP complexes by aiding the heptameric oligomerization of Sm proteins onto U snRNAs. Using in vitro Sm core assembly assays, we found that lowering the intracellular amounts of Gemin3 by either poliovirus infection or small interfering RNA (siRNA)-mediated knockdown of Gemin3 resulted in reduced assembly of U snRNPs. Immunofluorescence analyses revealed a specific redistribution of Sm proteins from the nucleoplasm to the cytoplasmic periphery of the nucleus in poliovirus-infected cells. We propose that defects in U snRNP assembly may be shared features of SMA and poliomyelitis.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Majewski, Pawel W.; Yager, Kevin G.

Block-copolymers self-assemble into diverse morphologies, where nanoscale order can be finely tuned via block architecture and processing conditions. However, the ultimate usage of these materials in real-world applications may be hampered by the extremely long thermal annealing times—hours or days—required to achieve good order. Here, we provide an overview of the fundamentals of block-copolymer self-assembly kinetics, and review the techniques that have been demonstrated to influence, and enhance, these ordering kinetics. We discuss the inherent tradeoffs between oven annealing, solvent annealing, microwave annealing, zone annealing, and other directed self-assembly methods; including an assessment of spatial and temporal characteristics. Here, wemore » also review both real-space and reciprocal-space analysis techniques for quantifying order in these systems.« less

Drug delivery by water-soluble organometallic cages.

PubMed

Therrien, Bruno

2012-01-01

Until recently, organometallic derivatives were generally viewed as moisture- and air-sensitive compounds, and consequently very challenging to synthesise and very demanding in terms of laboratory requirements (Schlenk techniques, dried solvent, glove box). However, an increasing number of stable, water-soluble organometallic compounds are now available, and organometallic chemistry in aqueous phase is a flourishing area of research. As such, coordination-driven self-assemblies using organometallic building blocks are compatible with water, thus opening new perspectives in bio-organometallic chemistry.This chapter gives a short history of coordination-driven self-assembly, with a special attention to organometallic metalla-cycles, especially those composed of half-sandwich complexes. These metalla-assemblies have been used as sensors, as anticancer agents, as well as drug carriers.

Numerical approach on dynamic self-assembly of colloidal particles

NASA Astrophysics Data System (ADS)

Ibrahimi, Muhamet; Ilday, Serim; Makey, Ghaith; Pavlov, Ihor; Yavuz, Özgàn; Gulseren, Oguz; Ilday, Fatih Omer

Far from equilibrium systems of artificial ensembles are crucial for understanding many intelligent features in self-organized natural systems. However, the lack of established theory underlies a need for numerical implementations. Inspired by a novel work, we simulate a solution-suspended colloidal system that dynamically self assembles due to convective forces generated in the solvent when heated by a laser. In order to incorporate with random fluctuations of particles and continuously changing flow, we exploit a random-walk based Brownian motion model and a fluid dynamics solver prepared for games, respectively. Simulation results manage to fit to experiments and show many quantitative features of a non equilibrium dynamic self assembly, including phase space compression and an ensemble-energy input feedback loop.

Organic supernanostructures self-assembled via solution process for explosive detection.

PubMed

Wang, Lei; Zhou, Yan; Yan, Jing; Wang, Jian; Pei, Jian; Cao, Yong

2009-02-03

Three different polymorphic crystalline structures, including microbelts and flowerlike supernanostructures, were obtained via a simple solution process by utilizing different solvents from an oligoarene derivative. Explosive chemosensors based on these self-assembled organic crystalline nanostructures were successfully fabricated. The differences in the structures on the microscopic level and in the film morphologies led to dramatic enhancements of the explosive detection speed. With the evolution of structures from the netted 1D microbelts to the flowerlike supernanostructures, the detection speed of the chemosensors for DNT and TNT was improved by more than 700 times. Our discovery demonstrates that the morphology control through self-assembly provides a new platform to utilize organic crystalline microstructures for chemosensors, optoelectronics, biosensors and bioelectronics, and so forth.

Rapid ordering of block copolymer thin films

NASA Astrophysics Data System (ADS)

Majewski, Pawel W.; Yager, Kevin G.

2016-10-01

Block-copolymers self-assemble into diverse morphologies, where nanoscale order can be finely tuned via block architecture and processing conditions. However, the ultimate usage of these materials in real-world applications may be hampered by the extremely long thermal annealing times—hours or days—required to achieve good order. Here, we provide an overview of the fundamentals of block-copolymer self-assembly kinetics, and review the techniques that have been demonstrated to influence, and enhance, these ordering kinetics. We discuss the inherent tradeoffs between oven annealing, solvent annealing, microwave annealing, zone annealing, and other directed self-assembly methods; including an assessment of spatial and temporal characteristics. We also review both real-space and reciprocal-space analysis techniques for quantifying order in these systems.

Harnessing Thin-Film Continuous-Flow Assembly Lines.

PubMed

Britton, Joshua; Castle, Jared W; Weiss, Gregory A; Raston, Colin L

2016-07-25

Inspired by nature's ability to construct complex molecules through sequential synthetic transformations, an assembly line synthesis of α-aminophosphonates has been developed. In this approach, simple starting materials are continuously fed through a thin-film reactor where the intermediates accrue molecular complexity as they progress through the flow system. Flow chemistry allows rapid multistep transformations to occur via reaction compartmentalization, an approach not amenable to using conventional flasks. Thin film processing can also access facile in situ solvent exchange to drive reaction efficiency, and through this method, α-aminophosphonate synthesis requires only 443 s residence time to produce 3.22 g h(-1) . Assembly-line synthesis allows unprecedented reaction flexibility and processing efficiency. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Evidence for adverse reproductive outcomes among women microelectronic assembly workers.

PubMed Central

Huel, G; Mergler, D; Bowler, R

1990-01-01

Microelectronics assembly entails complex processes where several potentially fetotoxic chemical compounds are used extensively. This study was undertaken to assess the potential adverse reproductive outcomes among former women workers in a microelectronics assembly plant in New Mexico with respect to a comparable population from the same geographical region and to examine the relation between these outcomes and employment history in this plant. After matching a pool of 143 former microelectronic female workers and 105 referents, 90 former microelectronic female worker-referent pairs were constituted (representing 302 and 324 pregnancies in former workers and referents respectively). The odds ratio (for pair matching design) of spontaneous abortion among women workers, before beginning to assemble microelectronic components, was 0.9 (chi 2 = 0.04; NS). After the beginning of employment this odds ratio became 5.6 (chi 2 = 9.8; p less than 1%). This estimated odds ratio decreased to 4.0, taking into account the increased risk for spontaneous abortion in previous pregnancies before employment (chi 2 = 5.4; p less than 5%). It was not possible to determine if this effect was reversible owing to the small number of pairs available after employment. The findings of this study corroborate the results of former studies that suggest a potential association between electronic manufacturing activity and risk of spontaneous abortion. Although the organic solvents were suspected of being the potential risk factor, this study was inconclusive from this point of view. Nevertheless, these investigations may provide some insight into reproductive outcomes among female workers exposed to solvents. PMID:2378817

Theory and modeling of particles with DNA-mediated interactions

NASA Astrophysics Data System (ADS)

Licata, Nicholas A.

2008-05-01

In recent years significant attention has been attracted to proposals which utilize DNA for nanotechnological applications. Potential applications of these ideas range from the programmable self-assembly of colloidal crystals, to biosensors and nanoparticle based drug delivery platforms. In Chapter I we introduce the system, which generically consists of colloidal particles functionalized with specially designed DNA markers. The sequence of bases on the DNA markers determines the particle type. Due to the hybridization between complementary single-stranded DNA, specific, type-dependent interactions can be introduced between particles by choosing the appropriate DNA marker sequences. In Chapter II we develop a statistical mechanical description of the aggregation and melting behavior of particles with DNA-mediated interactions. In Chapter III a model is proposed to describe the dynamical departure and diffusion of particles which form reversible key-lock connections. In Chapter IV we propose a method to self-assemble nanoparticle clusters using DNA scaffolds. A natural extension is discussed in Chapter V, the programmable self-assembly of nanoparticle clusters where the desired cluster geometry is encoded using DNA-mediated interactions. In Chapter VI we consider a nanoparticle based drug delivery platform for targeted, cell specific chemotherapy. In Chapter VII we present prospects for future research: the connection between DNA-mediated colloidal crystallization and jamming, and the inverse problem in self-assembly.

Robust forests of vertically aligned carbon nanotubes chemically assembled on carbon substrates.

PubMed

Garrett, David J; Flavel, Benjamin S; Shapter, Joseph G; Baronian, Keith H R; Downard, Alison J

2010-02-02

Forests of vertically aligned carbon nanotubes (VACNTs) have been chemically assembled on carbon surfaces. The structures show excellent stability over a wide potential range and are resistant to degradation from sonication in acid, base, and organic solvent. Acid-treated single-walled carbon nanotubes (SWCNTs) were assembled on amine-terminated tether layers covalently attached to pyrolyzed photoresist films. Tether layers were electrografted to the carbon substrate by reduction of the p-aminobenzenediazonium cation and oxidation of ethylenediamine. The amine-modified surfaces were incubated with cut SWCNTs in the presence of N,N'-dicyclohexylcarbodiimide (DCC), giving forests of vertically aligned carbon nanotubes (VACNTs). The SWCNT assemblies were characterized by scanning electron microscopy, atomic force microscopy, and electrochemistry. Under conditions where the tether layers slow electron transfer between solution-based redox probes and the underlying electrode, the assembly of VACNTs on the tether layer dramatically increases the electron-transfer rate at the surface. The grafting procedure, and hence the preparation of VACNTs, is applicable to a wide range of materials including metals and semiconductors.

Dimensional control of supramolecular assemblies of diacetylene-derived peptide gemini amphiphile: from spherical micelles to foamlike networks.

PubMed

Jiang, Hao; Ehlers, Martin; Hu, Xiao-Yu; Zellermann, Elio; Schmuck, Carsten

2018-05-22

Peptide amphiphiles capable of assembling into multidimensional nanostructures have attracted much attention over the past decade due to their potential applications in materials science. Herein, a novel diacetylene-derived peptide gemini amphiphile with a fluorenylmethyloxycarbonyl (Fmoc) group at the N-terminus is reported to hierarchically assemble into spherical micelles, one-dimensional nanorods, two-dimensional foamlike networks and lamellae. Solvent polarity shows a remarkable effect on the self-assembled structures by changing the balance of four weak noncovalent interactions (hydrogen-bonding, π-π stacking, hydrophobic interaction, and electrostatic repulsion). We also show the time-evolution not only from spherical micelles to helical nanofibers in aqueous solution, but also from branched wormlike micelles to foamlike networks in methanol solution. In this work, the presence of the Fmoc group plays a key role in the self-assembly process. This work provides an efficient strategy for precise morphological control, aiding the future development in materials science.

Role of Colloidal Drug Delivery Carriers in Taxane-mediated Chemotherapy: A Review.

PubMed

Kumar, Pramod; Raza, Kaisar; Kaushik, Lokesh; Malik, Ruchi; Arora, Shweta; Katare, Om Prakash

2016-01-01

Chemotherapy is one of the most frequently employed and reliable treatment options for the management of a variety of cancers. Taxanes (paclitaxel, docetaxel and cabazitaxel) are frequently prescribed to treat breast cancer, hormone refractory prostate cancer, non-small cell lung cancer and ovarian cancer. Most of the commercial products of taxanes are available as injectables, which are not patient compliant and are associated with frequent side effects like ototoxicity, baldness and neurotoxicity. Most of these concerns are ascribable to the presence of toxic solvents in these commercial formulations, which are used to solubilize these drug(s). However, there have been several attempts to develop toxic solvent free taxane formulations, especially employing novel drug delivery systems (NDDS). These systems have been reported to result in the advancement of anticancer activity, therapeutic index, stability, biocompatibility, tissue or organ targeting, encapsulation capacity, tissue permeability, oral bioavailability, reduced toxicity and reduced incidences of abnormal reactions, sustained and controlled release in comparison to the conventional solvent-based formulations. The review is an attempt to analyze the potential of NDDS-mediated taxane delivery for safer and effective cancer chemotherapy.

Membrane-Mediated Cooperativity of Proteins

NASA Astrophysics Data System (ADS)

Weikl, Thomas R.

2018-04-01

Besides direct protein-protein interactions, indirect interactions mediated by membranes play an important role for the assembly and cooperative function of proteins in membrane shaping and adhesion. The intricate shapes of biological membranes are generated by proteins that locally induce membrane curvature. Indirect curvature-mediated interactions between these proteins arise because the proteins jointly affect the bending energy of the membranes. These curvature-mediated interactions are attractive for crescent-shaped proteins and are a driving force in the assembly of the proteins during membrane tubulation. Membrane adhesion results from the binding of receptor and ligand proteins that are anchored in the apposing membranes. The binding of these proteins strongly depends on nanoscale shape fluctuations of the membranes, leading to a fluctuation-mediated binding cooperativity. A length mismatch between receptor-ligand complexes in membrane adhesion zones causes repulsive curvature-mediated interactions that are a driving force for the length-based segregation of proteins during membrane adhesion.

Fast self-assembly of silver nanoparticle monolayer in hydrophobic environment and its application as SERS substrate

NASA Astrophysics Data System (ADS)

Leiterer, Christian; Zopf, David; Seise, Barbara; Jahn, Franka; Weber, Karina; Popp, Jürgen; Cialla-May, Dana; Fritzsche, Wolfgang

2014-09-01

We present a method which allows the straightforward wet-chemical synthesis of silver nanoparticles (AgNPs), hydrophobic coating assembling into monolayer, and their utilization as substrates for surface-enhanced Raman spectroscopy (SERS). In order to fabricate the SERS-active substrates, AgNPs were synthesized in water by chemical reduction of Ag+, coated with a hydrophobic shell (dodecanethiol), transferred to a non-polar solvent, and finally assembled through precipitation into a SERS-active self-assembled monolayer (SAM). Simple approaches for concentration and purification of the coated AgNPs are shown. The synthesized particles and SAMs were characterized by transmission electron microscopy, optical imaging, and spectroscopic measurements. This manuscript can be used as a do-it-yourself (DIY) tutorial which allows making SAMs from coated AgNPs (<15 nm) in every laboratory within less than 1 h and their utilization as potential low-cost SERS substrates (movie 1-4).

Self-assembly modes of glycyrrhetinic acid esters in view of the crystal packing of related triterpene molecules.

PubMed

Langer, Dominik; Wicher, Barbara; Szczołko, Wojciech; Gdaniec, Maria; Tykarska, Ewa

2016-08-01

The crystal structures of three ester derivatives of glycyrrhetinic acid (GE) are reported. X-ray crystallography revealed that despite differences in the size of the ester substituents (ethyl, isopropyl and 2-morpholinoethyl) the scheme of molecular self-assembly is similar in all three cases but differs significantly from that observed in other known GE esters. According to our analysis, the two basic patterns of self-assembly of GE esters observed in their unsolvated crystals correspond to two distinct orientations of the ester groups relative to the triterpene backbone. Moreover, comparison of the self-assembly modes of GE esters in their unsolvated forms with the supramolecular organization of GE and carbenoxolone in their solvated crystals revealed that ester substituents replace solvent molecules hydrogen bonded to the COOH group at the triterpene skeleton, resulting in similar packing arrangements of these compounds.

In Situ Visualization of Block Copolymer Self‐Assembly in Organic Media by Super‐Resolution Fluorescence Microscopy

PubMed Central

Boott, Charlotte E.; Laine, Romain F.; Mahou, Pierre; Finnegan, John R.; Leitao, Erin M.

2015-01-01

Abstract Analytical methods that enable visualization of nanomaterials derived from solution self‐assembly processes in organic solvents are highly desirable. Herein, we demonstrate the use of stimulated emission depletion microscopy (STED) and single molecule localization microscopy (SMLM) to map living crystallization‐driven block copolymer (BCP) self‐assembly in organic media at the sub‐diffraction scale. Four different dyes were successfully used for single‐colour super‐resolution imaging of the BCP nanostructures allowing micelle length distributions to be determined in situ. Dual‐colour SMLM imaging was used to measure and compare the rate of addition of red fluorescent BCP to the termini of green fluorescent seed micelles to generate block comicelles. Although well‐established for aqueous systems, the results highlight the potential of super‐resolution microscopy techniques for the interrogation of self‐assembly processes in organic media. PMID:26477697

Coassembly of Lysozyme and Amphiphilic Biomolecules Driven by Unimer-Aggregate Equilibrium.

PubMed

Tao, Yuanyuan; Ma, Xiaoteng; Cai, Yaqian; Liu, Li; Zhao, Hanying

2018-04-12

Synthesis and self-assembly of bioconjugates composed of proteins and synthetic molecules have been widely studied because of the potential applications in medicine, biotechnology, and nanotechnology. One of the challenging research studies in this area is to develop organic solvent-free approaches to the synthesis and self-assembly of amphiphilic bioconjugates. In this research, dialysis-assisted approach, a method based on unimer-aggregate equilibrium, was applied in the coassembly of lysozyme and conjugate of cholesterol and glutathione (Ch-GSH). In phosphate buffer solution, amphiphilic Ch-GSH conjugate self-assembles into vesicles, and the vesicle solution is dialyzed against lysozyme solution. Negatively charged Ch-GSH unimers produced in the unimer-vesicle exchange equilibrium, diffuse across the dialysis membrane and have electrostatic interaction with positively charged lysozyme, resulting in the formation of Ch-GSH-lysozyme bioconjugate. Above a critical concentration, the three-component bioconjugate molecules self-assemble into bioactive vesicles.

Nanocrystalline Precursors for the Co-Assembly of Crack-Free Metal Oxide Inverse Opals.

PubMed

Phillips, Katherine R; Shirman, Tanya; Shirman, Elijah; Shneidman, Anna V; Kay, Theresa M; Aizenberg, Joanna

2018-05-01

Inorganic microstructured materials are ubiquitous in nature. However, their formation in artificial self-assembly systems is challenging as it involves a complex interplay of competing forces during and after assembly. For example, colloidal assembly requires fine-tuning of factors such as the size and surface charge of the particles and electrolyte strength of the solvent to enable successful self-assembly and minimize crack formation. Co-assembly of templating colloidal particles together with a sol-gel matrix precursor material helps to release stresses that accumulate during drying and solidification, as previously shown for the formation of high-quality inverse opal (IO) films out of amorphous silica. Expanding this methodology to crystalline materials would result in microscale architectures with enhanced photonic, electronic, and catalytic properties. This work describes tailoring the crystallinity of metal oxide precursors that enable the formation of highly ordered, large-area (mm 2 ) crack-free titania, zirconia, and alumina IO films. The same bioinspired approach can be applied to other crystalline materials as well as structures beyond IOs. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

NSF- and SNARE-mediated membrane fusion is required for nuclear envelope formation and completion of nuclear pore complex assembly in Xenopus laevis egg extracts.

PubMed

Baur, Tina; Ramadan, Kristijan; Schlundt, Andreas; Kartenbeck, Jürgen; Meyer, Hemmo H

2007-08-15

Despite the progress in understanding nuclear envelope (NE) reformation after mitosis, it has remained unclear what drives the required membrane fusion and how exactly this is coordinated with nuclear pore complex (NPC) assembly. Here, we show that, like other intracellular fusion reactions, NE fusion in Xenopus laevis egg extracts is mediated by SNARE proteins that require activation by NSF. Antibodies against Xenopus NSF, depletion of NSF or the dominant-negative NSF(E329Q) variant specifically inhibited NE formation. Staging experiments further revealed that NSF was required until sealing of the envelope was completed. Moreover, excess exogenous alpha-SNAP that blocks SNARE function prevented membrane fusion and caused accumulation of non-flattened vesicles on the chromatin surface. Under these conditions, the nucleoporins Nup107 and gp210 were fully recruited, whereas assembly of FxFG-repeat-containing nucleoporins was blocked. Together, we define NSF- and SNARE-mediated membrane fusion events as essential steps during NE formation downstream of Nup107 recruitment, and upstream of membrane flattening and completion of NPC assembly.

Benzyl alcohol and block copolymer micellar lithography: a versatile route to assembling gold and in situ generated titania nanoparticles into uniform binary nanoarrays.

PubMed

Polleux, Julien; Rasp, Matthias; Louban, Ilia; Plath, Nicole; Feldhoff, Armin; Spatz, Joachim P

2011-08-23

Simultaneous synthesis and assembly of nanoparticles that exhibit unique physicochemical properties are critically important for designing new functional devices at the macroscopic scale. In the present study, we report a simple version of block copolymer micellar lithography (BCML) to synthesize gold and titanium dioxide (TiO(2)) nanoarrays by using benzyl alcohol (BnOH) as a solvent. In contrast to toluene, BnOH can lead to the formation of various gold nanopatterns via salt-induced micellization of polystyrene-block-poly(vinylpyridine) (PS-b-P2VP). In the case of titania, the use of BCML with a nonaqueous sol-gel method, the "benzyl alcohol route", enables the fabrication of nanopatterns made of quasi-hexagonally organized particles or parallel wires upon aging a (BnOH-TiCl(4)-PS(846)-b-P2VP(171))-containing solution for four weeks to grow TiO(2) building blocks in situ. This approach was found to depend mainly on the relative lengths of the polymer blocks, which allows nanoparticle-induced micellization and self-assembly during solvent evaporation. Moreover, this versatile route enables the design of uniform and quasi-ordered gold-TiO(2) binary nanoarrays with a precise particle density due to the absence of graphoepitaxy during the deposition of TiO(2) onto gold nanopatterns. © 2011 American Chemical Society

Biodegradable self-assembled PEG-PCL-PEG micelles for hydrophobic honokiol delivery: I. Preparation and characterization

NASA Astrophysics Data System (ADS)

Gong, ChangYang; Wei, XiaWei; Wang, XiuHong; Wang, YuJun; Guo, Gang; Mao, YongQiu; Luo, Feng; Qian, ZhiYong

2010-05-01

This study aims to develop self-assembled poly(ethylene glycol)-poly(ɛ-caprolactone)-poly(ethylene glycol) (PEG-PCL-PEG, PECE) micelles to encapsulate hydrophobic honokiol (HK) in order to overcome its poor water solubility and to meet the requirement of intravenous administration. Honokiol loaded micelles (HK-micelles) were prepared by self-assembly of PECE copolymer in aqueous solution, triggered by its amphiphilic characteristic assisted by ultrasonication without any organic solvents, surfactants and vigorous stirring. The particle size of the prepared HK-micelles measured by Malvern laser particle size analyzer were 58 nm, which is small enough to be a candidate for an intravenous drug delivery system. Furthermore, the HK-micelles could be lyophilized into powder without any adjuvant, and the re-dissolved HK-micelles are stable and homogeneous with particle size about 61 nm. Furthermore, the in vitro release profile showed a significant difference between the rapid release of free HK and the much slower and sustained release of HK-micelles. Moreover, the cytotoxicity results of blank micelles and HK-micelles showed that the PECE micelle was a safe carrier and the encapsulated HK retained its potent antitumor effect. In short, the HK-micelles were successfully prepared by an improved method and might be promising carriers for intravenous delivery of HK in cancer chemotherapy, being effective, stable, safe (organic solvent and surfactant free), and easy to produce and scale up.

Formation of thin film like assembly of exfoliated C3N4 nanoflakes by solvent non-evaporative method using centrifuge

NASA Astrophysics Data System (ADS)

Tejasvi, Ravi; Basu, Suddhasatwa

2017-12-01

A simple method for depositing a thin film of nanomaterial on a substrate using centrifugation technique has been developed, whereby solvent evaporation is prevented and solvent reuse is possible. The centrifuge technique of deposition yields uniform, smooth thin film irrespective of substrate surface texture. The deposited TiO2/eC3N4 film studied, through field emission scanning electron microscope, atomic force microscope, and optical surface profilometer, shows variation in surface roughness on the basis of centrifugation speeds. Initially film coverage improves and surface roughness decreases with the increase in rpm of the centrifuge and the surface roughness slightly increases with further increase in rpm. The photoelectrochemical studies of TiO2/eC3N4 films suggest that the centrifuge technique forms better heterojunctions compared to that by spin coating technique leading to enhanced photoelectrochemical water splitting.

X-ray photoelectron spectroscopy study of para-substituted benzoic acids chemisorbed to aluminum oxide thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kreil, Justin; Ellingsworth, Edward; Szulczewski, Greg

A series of para-substituted, halogenated (F, Cl, Br, and I) benzoic acid monolayers were prepared on the native oxide of aluminum surfaces by solution self-assembly and spin-coating techniques. The monolayers were characterized by x-ray photoelectron spectroscopy (XPS) and water contact angles. Several general trends are apparent. First, the polarity of the solvent is critical to monolayer formation. Protic polar solvents produced low coverage monolayers; in contrast, nonpolar solvents produced higher coverage monolayers. Second, solution deposition yields a higher surface coverage than spin coating. Third, the thickness of the monolayers determined from XPS suggests the plane of the aromatic ring ismore » perpendicular to the surface with the carboxylate functional group most likely binding in a bidentate chelating geometry. Fourth, the saturation coverage (∼2.7 × 10{sup 14} molecules cm{sup −2}) is independent of the para-substituent.« less

Solvent-induced assembly of two helical Eu(III) metal-organic frameworks and fluorescence sensing activities towards nitrobenzene and Cu2+ ions

NASA Astrophysics Data System (ADS)

Ma, Ranran; Chen, Zhiwei; Wang, Suna; Yao, Qingxia; Li, Yunwu; Lu, Jing; Li, Dacheng; Dou, Jianmin

2017-08-01

Two helical Eu(III) metal-organic frameworks, namely, {[Eu(L)(DMF)(H2O)]·0.5DMF}n (1) and [Eu(L)(DEF)(H2O)]n (2) (H3L=3,5-bis(2-carboxylphenoxy)benzoic acid, DMF=N,N-dimethylformamide, DEF=N,N-diethylformamide), have been solvothermally synthesized in different solvents, respectively. Both complexes possess helical structures through the connectivity of Eu atoms and phenolic-oxygen containing branches of the flexible multicarboxylate ligand. Based on different helices, these two complexes exhibited hexagonal and tetragonal channels, respectively. Both complexes possess (3,6)-connected (4.62)2(42.610.83) topology but with different long Schlafli symbol. The solvent plays an important role in the formation of the final frameworks. Both complexes can sensitively and selectively detect nitrobenzene and Cu2+ ions.

Solvent relaxation of fluorescent labels as a new tool for the detection of polarity and rigidity changes in membranes

NASA Astrophysics Data System (ADS)

Hof, Martin; Hutterer, Rudi

1998-04-01

Since solvent relaxation (SR) exclusively depends on the physical properties of the dye environment, SR spectroscopy of defined located labels in amphiphilic assemblies accomplishes the characterisation of specific domains. The most accurate way to characterise SR is the determination of the time-dependent Stokes shift. The time course of the Stokes shift, expressed as a solvent relaxation time, gives information about both the rigidity and polarity of the dye environment. The absolute value of the Stokes shift following the excitation is correlated with the polarity of the probed region. The validity of this approach for the investigation of phospholipid bilayers is illustrated by listing the parameters influencing the SR kinetics of appropriate membrane labels: membrane curvature, percentage of phosphatidylserine (PS) in small unilamell vesicles (SUV), addition of Ca2+ ions, binding of vitamin-K dependent proteins, percentage of diether-lipids in phosphatidylcholine (PC)-vesicles, and temperature.

Polymer nano-particle hybrid micelles: Encapsulation of POSS into semi-fluorinated polymer micelles

NASA Astrophysics Data System (ADS)

Ratnaweera, Dilru; Perahia, Dvora; Iacono, Scott; Mabry, Joseph; Smith, Dennis

2012-02-01

Self-assembly of block copolymers in selective solvents was used to form a nanoparticle (NP)/polymer hybrid micelles. These micelles can be used as a cargo vehicle for other substances such as drug delivery, and as building blocks for polymer-nanocomposites with controlled NP distribution. Association of NPs into specific blocks of the copolymer depends on the compatibility between the NPs and the block as well as their preference to the solvent that micellization takes place. The current work introduces a small angle neutron scattering study of association of Polyhedral Oligomeric Silsesquioxane (POSS) NPs into micelles of a highly segregating random copolymer, Biphenyl Perfluorocyclobutane (BPh-PFCB), in toluene, which is a good solvent for BPh. Incompatibility between the blocks drives copolymer into micelles with PFCB in the core and BPh in swollen corona. Modification of NPs with polymer chains drives POSS cages into the micelle core and prevents the micelle dissociation at higher temperatures.

Regulation of Chromatin Assembly and Cell Transformation by Formaldehyde Exposure in Human Cells

PubMed Central

Chen, Danqi; Fang, Lei; Mei, Shenglin; Li, Hongjie; Xu, Xia; Des Marais, Thomas L.; Lu, Kun; Liu, X. Shirley

2017-01-01

Background: Formaldehyde (FA) is an environmental and occupational chemical carcinogen. Recent studies have shown that exogenous FA causes only a modest increase in DNA adduct formation compared with the amount of adducts formed by endogenous FA, raising the possibility that epigenetic mechanisms may contribute to FA-mediated carcinogenicity. Objectives: We investigated the effects of FA exposure on histone modifications and chromatin assembly. We also examined the role of defective chromatin assembly in FA-mediated transcription and cell transformation. Methods: Cellular fractionation and Western blot analysis were used to measure the levels of histone modifications in human bronchial epithelial BEAS-2B cells and human nasal RPMI2650 cells in the presence of FA. Chromatin immunoprecipitation (ChIP) and micrococcal nuclease (MNase) digest assays were performed to examine the changes in chromatin assembly and accessibility after FA exposure. RNA sequencing (RNA-seq) and real-time polymerase chain reaction (PCR) were used to examine transcriptional dysregulation. Finally, anchorage-independent cell growth ability was tested by soft agar assay following FA exposure. Results: Exposure to FA dramatically decreased the acetylation of the N-terminal tails of cytosolic histones. These modifications are important for histone nuclear import and subsequent chromatin assembly. Histone proteins were depleted in both the chromatin fraction and at most of the genomic loci tested following FA exposure, suggesting that FA compromises chromatin assembly. Moreover, FA increased chromatin accessibility and altered the expression of hundreds of cancer-related genes. Knockdown of the histone H3.3 gene (an H3 variant), which mimics inhibition of chromatin assembly, facilitated FA-mediated anchorage-independent cell growth. Conclusions: We propose that the inhibition of chromatin assembly represents a novel mechanism of cell transformation induced by the environmental and occupational chemical carcinogen FA. https://doi.org/10.1289/EHP1275 PMID:28937961

Bicontinuous mesoporous carbon thin films via an order-order transition.

PubMed

Deng, Guodong; Zhang, Yuanzhong; Ye, Changhuai; Qiang, Zhe; Stein, Gila E; Cavicchi, Kevin A; Vogt, Bryan D

2014-10-28

Bicontinuous mesoporous carbon films are fabricated by cooperative self-assembly of phenolic resin and amphiphilic triblock copolymer via an order-order transition from cylinders to gyroid. The film morphology is strongly influenced by the details of processing, including age of the resol, resol : template ratio, and the solvent vapor annealing process.

Method for synthesizing carbon nanotubes

DOEpatents

Fan, Hongyou

2012-09-04

A method for preparing a precursor solution for synthesis of carbon nanomaterials, where a polar solvent is added to at least one block copolymer and at least one carbohydrate compound, and the precursor solution is processed using a self-assembly process and subsequent heating to form nanoporous carbon films, porous carbon nanotubes, and porous carbon nanoparticles.

Self-assembly of block copolymers into sieve-like particles with arrayed switchable channels and as scaffolds to guide the arrangement of gold nanoparticles.

PubMed

He, Yun; Zhang, Yan; Yan, Nan; Zhu, Yutian; Jiang, Wei; Shi, Dean

2017-10-12

Well-defined polymeric particles with not only a controllable shape and internal nanostructures but also stimuli-responsive functions have attracted intensive attention because of their great potential in various fields. Herein, we created unique sieve-like particles with lattice arrayed switchable channels via the confined self-assembly of poly(4-vinylpyridine)-b-polystyrene-b-poly(4-vinylpyridine) (P4VP-b-PS-b-P4VP) triblock copolymers within the emulsion droplets and the subsequent swelling treatment in ethanol. It is worth noting that the hexagonally packed P4VP channels in the sieve-like particles are switched on and off by changing the solvent type, i.e., P4VP channels are switched on in ethanol and switched off in water, which can operate as a solvent-controlled chemical gate. Moreover, the well-defined sieve-like particles can be further used as scaffolds to guide the spatial arrangement of gold nanoparticles, which generates hybrid nanomaterials with controllable morphology and ordered spatial arrangement of AuNPs.

A priori calculations of the free energy of formation from solution of polymorphic self-assembled monolayers

PubMed Central

Reimers, Jeffrey R.; Panduwinata, Dwi; Visser, Johan; Chin, Yiing; Tang, Chunguang; Goerigk, Lars; Ford, Michael J.; Sintic, Maxine; Sum, Tze-Jing; Coenen, Michiel J. J.; Hendriksen, Bas L. M.; Elemans, Johannes A. A. W.; Hush, Noel S.; Crossley, Maxwell J.

2015-01-01

Modern quantum chemical electronic structure methods typically applied to localized chemical bonding are developed to predict atomic structures and free energies for meso-tetraalkylporphyrin self-assembled monolayer (SAM) polymorph formation from organic solution on highly ordered pyrolytic graphite surfaces. Large polymorph-dependent dispersion-induced substrate−molecule interactions (e.g., −100 kcal mol−1 to −150 kcal mol−1 for tetratrisdecylporphyrin) are found to drive SAM formation, opposed nearly completely by large polymorph-dependent dispersion-induced solvent interactions (70–110 kcal mol−1) and entropy effects (25–40 kcal mol−1 at 298 K) favoring dissolution. Dielectric continuum models of the solvent are used, facilitating consideration of many possible SAM polymorphs, along with quantum mechanical/molecular mechanical and dispersion-corrected density functional theory calculations. These predict and interpret newly measured and existing high-resolution scanning tunnelling microscopy images of SAM structure, rationalizing polymorph formation conditions. A wide range of molecular condensed matter properties at room temperature now appear suitable for prediction and analysis using electronic structure calculations. PMID:26512115

Solution-processed field-effect transistors based on dihexylquaterthiophene films with performances exceeding those of vacuum-sublimed films.

PubMed

Leydecker, Tim; Trong Duong, Duc; Salleo, Alberto; Orgiu, Emanuele; Samorì, Paolo

2014-12-10

Solution-processable oligothiophenes are model systems for charge transport and fabrication of organic field-effect transistors (OFET) . Herein we report a structure vs function relationship study focused on the electrical characteristics of solution-processed dihexylquaterthiophene (DH4T)-based OFET. We show that by combining the tailoring of all interfaces in the bottom-contact bottom-gate transistor, via chemisorption of ad hoc molecules on electrodes and dielectric, with suitable choice of the film preparation conditions (including solvent type, concentration, volume, and deposition method), it is possible to fabricate devices exhibiting field-effect mobilities exceeding those of vacuum-processed DH4T transistors. In particular, the evaporation rate of the solvent, the processing temperature, as well as the concentration of the semiconducting material were found to hold a paramount importance in driving the self-assembly toward the formation of highly ordered and low-dimensional supramolecular architectures, confirming the kinetically governed nature of the self-assembly process. Among the various architectures, hundreds-of-micrometers long and thin DH4T crystallites exhibited enhanced charge transport.

Low-temperature resistant, elastic adhesives and sealants for gas tank insulation

NASA Astrophysics Data System (ADS)

Karrer, R.

The leading European insulating firms in the domain of liquid natural gas (LNG)/liquid petroleum gas (LPG) carriers have developed special sandwich elements for the insulation of liquid gas tanks. The trend to increasing tank volumes and, at the same time, to reducing the number of cargo tanks in modern liquid gas carriers with loading capacities of up to 135,000 m 3 has in some cases entailed major changes with respect to tank design (Kaefer-Isoliertechnik, Hansa Schiffahrt-Schiffbau-Hafen, 133rd year, 1996, 2, 20-22). These changes have equally influenced both the design and the assembly of the panels used for insulation, as well as the adhesives and sealants applied for this purpose. This article describes the requirement profile and the possible applications of solvent-free two-component polyurethane adhesives (2-K PU) and recently developed polyurethane hot-melt adhesives (PU-HM) for the manufacture and/or assembly of panels. Moreover, it deals with the role of the advanced solvent-free, silane-modified polymers (MS polymers) in the pointing of panels (seam-sealing) exposed to low temperatures.

Synthesis, self-assembly, and properties of Mn doped ZnO nanoparticles.

PubMed

Barick, K C; Bahadur, D

2007-06-01

We report here a novel process to prepare Mn doped ZnO nanoparticles by a soft chemical route at low temperature. The synthesis process is based on the hydrolysis of zinc acetate dihydrate and manganese acetate tetrahydrate heated under reflux to 160-175 degrees C using diethylene glycol as a solvent. X-ray diffraction analysis reveals that the Mn doped ZnO crystallizes in a wurtzite structure with crystal size of 15-25 nm. These nano size crystallites of Mn doped ZnO self-organize into polydisperse spheres in size ranging from 100-400 nm. Transmission Electron Microscopy image also shows that each sphere is made up of numerous nanocrystals of average diameter 15-25 nm. By means of X-ray photoelectron spectroscopy and electron spin resonance spectroscopy, we determined the valence state of Mn ions as 2+. These nanoparticles were found to be ferromagnetic at room temperature. Monodisperse porous spheres (approximately 250 nm) were obtained by size selective separation technique and then self-assembled in a closed pack periodic array through sedimentation with slow solvent evaporation, which gives strong opalescence in visible region.

Anionic membrane and ionomer based on poly(2,6-dimethyl-1,4-phenylene oxide) for alkaline membrane fuel cells

NASA Astrophysics Data System (ADS)

Ong, Ai Lien; Saad, Saeed; Lan, Rong; Goodfellow, Robert J.; Tao, Shanwen

2011-10-01

Hydroxyl-ion conductive poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) membranes with different characteristics were prepared via relatively simple bromination/amination serial reactions with reduced number of involved chemicals and shorter reaction time. The effects of reactants ratio, reaction atmosphere, polymer concentration, casting solvent, and hydroxylation treatment on reaction were investigated in details. The microstructure, water uptake, swelling ratio, ion-exchange capacity and ionic conductivity of the membranes were also studied. The obtained results demonstrate that, the ionic conductivity of the membrane is dependent on casting solvent. The N-methyl-2-pyrrolidonecast membrane exhibits the highest conductivity with the thinnest film. Although the membrane was prepared via a relatively simple preparation route with least toxic chemicals, a competitive ionic conductivity value of 1.64 × 10-2 S cm-1 was achieved at 60 °C. A power density of 19.5 mW cm-2 has been demonstrated from the alkaline membrane fuel cell operated at 70 °C, assembled from the entirely homemade membrane electrode assembly without any hot-pressing.

Widely Tunable Morphologies in Block Copolymer Thin Films Through Solvent Vapor Annealing Using Mixtures of Selective Solvents

PubMed Central

Chavis, Michelle A.; Smilgies, Detlef-M.; Wiesner, Ulrich B.; Ober, Christopher K.

2015-01-01

Thin films of block copolymers are extremely attractive for nanofabrication because of their ability to form uniform and periodic nanoscale structures by microphase separation. One shortcoming of this approach is that to date the design of a desired equilibrium structure requires synthesis of a block copolymer de novo within the corresponding volume ratio of the blocks. In this work, we investigated solvent vapor annealing in supported thin films of poly(2-hydroxyethyl methacrylate)-block-poly(methyl methacrylate) [PHEMA-b-PMMA] by means of grazing incidence small angle X–ray scattering (GISAXS). A spin-coated thin film of lamellar block copolymer was solvent vapor annealed to induce microphase separation and improve the long-range order of the self-assembled pattern. Annealing in a mixture of solvent vapors using a controlled volume ratio of solvents (methanol, MeOH, and tetrahydrofuran, THF), which are chosen to be preferential for each block, enabled selective formation of ordered lamellae, gyroid, hexagonal or spherical morphologies from a single block copolymer with a fixed volume fraction. The selected microstructure was then kinetically trapped in the dry film by rapid drying. To our knowledge, this paper describes the first reported case where in-situ methods are used to study the transition of block copolymer films from one initial disordered morphology to four different ordered morphologies, covering much of the theoretical diblock copolymer phase diagram. PMID:26819574

Pwp2 mediates UTP-B assembly via two structurally independent domains.

PubMed

Boissier, Fanny; Schmidt, Christina Maria; Linnemann, Jan; Fribourg, Sébastien; Perez-Fernandez, Jorge

2017-06-09

The SSU processome constitutes a large ribonucleoprotein complex involved in the early steps of ribosome biogenesis. UTP-B is one of the first multi-subunit protein complexes that associates with the pre-ribosomal RNA to form the SSU processome. To understand the molecular basis of the hierarchical assembly of the SSU-processome, we have undergone a structural and functional analysis of the UTP-B subunit Pwp2p. We show that Pwp2p is required for the proper assembly of UTP-B and for a productive association of UTP-B with pre-rRNA. These two functions are mediated by two distinct structural domains. The N-terminal domain of Pwp2p folds into a tandem WD-repeat (tWD) that associates with Utp21p, Utp18p, and Utp6p to form a core complex. The CTDs of Pwp2p and Utp21p mediate the assembly of the heterodimer Utp12p:Utp13p that is required for the stable incorporation of the UTP-B complex in the SSU processome. Finally, we provide evidence suggesting a role of UTP-B as a platform for the binding of assembly factors during the maturation of 20S rRNA precursors.

Creating "hotels" for cells by electrospinning honeycomb-like polymeric structures.

PubMed

Liang, T; Mahalingam, S; Edirisinghe, M

2013-10-01

It is well established that three-dimensional honeycomb-like nanofibrous structures enhance cell activity. In this work, we report that electrospun polymer nanofibres self-assemble into three-dimensional honeycomb-like structures. The underlying mechanism is studied by varying the polymer solution concentration, collecting substrates and working distance. The polymer solution concentration has a significant effect on the size of the electrospun nanofibres. The collection substrate and working distance affect the electric field strength, the evaporation of solvent and the discharging of nanofibres and consequently these two had a significant influence on the self-assembly of nanofibres. © 2013.

Halogenated solvent remediation

DOEpatents

Sorenson, Kent S.

2004-08-31

Methods for enhancing bioremediation of ground water contaminated with nonaqueous halogenated solvents are disclosed. A preferred method includes adding a composition to the ground water wherein the composition is an electron donor for microbe-mediated reductive dehalogenation of the halogenated solvents and enhances mass transfer of the halogenated solvents from residual source areas into the aqueous phase of the ground water. Illustrative compositions effective in these methods include surfactants such as C.sub.2 -C.sub.4 carboxylic acids and hydroxy acids, salts thereof, esters of C.sub.2 -C.sub.4 carboxylic acids and hydroxy acids, and mixtures thereof. Especially preferred compositions for use in these methods include lactic acid, salts of lactic acid, such as sodium lactate, lactate esters, and mixtures thereof. The microbes are either indigenous to the ground water, or such microbes can be added to the ground water in addition to the composition.

Selective self-assembly of adenine-silver nanoparticles forms rings resembling the size of cells

NASA Astrophysics Data System (ADS)

Choi, Sungmoon; Park, Soonyoung; Yang, Seon-Ah; Jeong, Yujin; Yu, Junhua

2015-12-01

Self-assembly has played critical roles in the construction of functional nanomaterials. However, the structure of the macroscale multicomponent materials built by the self-assembly of nanoscale building blocks is hard to predict due to multiple intermolecular interactions of great complexity. Evaporation of solvents is usually an important approach to induce kinetically stable assemblies of building blocks with a large-scale specific arrangement. During such a deweting process, we tried to monitor the possible interactions between silver nanoparticles and nucleobases at a larger scale by epifluorescence microscopy, thanks to the doping of silver nanoparticles with luminescent silver nanodots. ssDNA oligomer-stabilized silver nanoparticles and adenine self-assemble to form ring-like compartments similar to the size of modern cells. However, the silver ions only dismantle the self-assembly of adenine. The rings are thermodynamically stable as the drying process only enrich the nanoparticles-nucleobase mixture to a concentration that activates the self-assembly. The permeable membrane-like edge of the ring is composed of adenine filaments glued together by silver nanoparticles. Interestingly, chemicals are partially confined and accumulated inside the ring, suggesting that this might be used as a microreactor to speed up chemical reactions during a dewetting process.

Self-assembly of diphenylalanine backbone homologues and their combination with functionalized carbon nanotubes.

PubMed

Dinesh, Bhimareddy; Squillaci, Marco A; Ménard-Moyon, Cécilia; Samorì, Paolo; Bianco, Alberto

2015-10-14

The integration of carbon nanotubes (CNTs) into organized nanostructures is of great interest for applications in materials science and biomedicine. In this work we studied the self-assembly of β and γ homologues of diphenylalanine peptides under different solvent and pH conditions. We aimed to investigate the role of peptide backbone in tuning the formation of different types of nanostructures alone or in combination with carbon nanotubes. In spite of having the same side chain, β and γ peptides formed distinctively different nanofibers, a clear indication of the role played by the backbone homologation on the self-assembly. The variation of the pH allowed to transform the nanofibers into spherical structures. Moreover, the co-assembly of β and γ peptides with carbon nanotubes covalently functionalized with the same peptide generated unique dendritic assemblies. This comparative study on self-assembly using diphenylalanine backbone homologues and of the co-assembly with CNT covalent conjugates is the first example exploring the capacity of β and γ peptides to adopt precise nanostructures, particularly in combination with carbon nanotubes. The dendritic organization obtained by mixing carbon nanotubes and peptides might find interesting applications in tissue engineering and neuronal interfacing.

Identification and Targeting of an Interaction between a Tyrosine Motif within Hepatitis C Virus Core Protein and AP2M1 Essential for Viral Assembly

PubMed Central

Ziv-Av, Amotz; Gerber, Doron; Jacob, Yves; Einav, Shirit

2012-01-01

Novel therapies are urgently needed against hepatitis C virus infection (HCV), a major global health problem. The current model of infectious virus production suggests that HCV virions are assembled on or near the surface of lipid droplets, acquire their envelope at the ER, and egress through the secretory pathway. The mechanisms of HCV assembly and particularly the role of viral-host protein-protein interactions in mediating this process are, however, poorly understood. We identified a conserved heretofore unrecognized YXXΦ motif (Φ is a bulky hydrophobic residue) within the core protein. This motif is homologous to sorting signals within host cargo proteins known to mediate binding of AP2M1, the μ subunit of clathrin adaptor protein complex 2 (AP-2), and intracellular trafficking. Using microfluidics affinity analysis, protein-fragment complementation assays, and co-immunoprecipitations in infected cells, we show that this motif mediates core binding to AP2M1. YXXΦ mutations, silencing AP2M1 expression or overexpressing a dominant negative AP2M1 mutant had no effect on HCV RNA replication, however, they dramatically inhibited intra- and extracellular infectivity, consistent with a defect in viral assembly. Quantitative confocal immunofluorescence analysis revealed that core's YXXΦ motif mediates recruitment of AP2M1 to lipid droplets and that the observed defect in HCV assembly following disruption of core-AP2M1 binding correlates with accumulation of core on lipid droplets, reduced core colocalization with E2 and reduced core localization to trans-Golgi network (TGN), the presumed site of viral particles maturation. Furthermore, AAK1 and GAK, serine/threonine kinases known to stimulate binding of AP2M1 to host cargo proteins, regulate core-AP2M1 binding and are essential for HCV assembly. Last, approved anti-cancer drugs that inhibit AAK1 or GAK not only disrupt core-AP2M1 binding, but also significantly inhibit HCV assembly and infectious virus production. These results validate viral-host interactions essential for HCV assembly and yield compounds for pharmaceutical development. PMID:22916011

The 38K-Mediated Specific Dephosphorylation of the Viral Core Protein P6.9 Plays an Important Role in the Nucleocapsid Assembly of Autographa californica Multiple Nucleopolyhedrovirus.

PubMed

Lai, Qingying; Wu, Wenbi; Li, Ao; Wang, Wei; Yuan, Meijin; Yang, Kai

2018-05-01

Encapsidation of the viral genomes, leading to the assembly of the nucleocapsids to form infectious progeny virions, is a key step in many virus life cycles. Baculovirus nucleocapsid assembly is a complex process that involves many proteins. Our previous studies showed that the deletion of the core gene 38K ( ac98 ) interrupted the nucleocapsid assembly by producing capsid sheaths devoid of viral genomes by an unknown mechanism. All homologs of 38K contain conserved motifs of the haloacid dehalogenase superfamily, which are involved in phosphoryl transfer. The requirements of these motifs for nucleocapsid assembly, confirmed in the present study, suggest that 38K may be a functioning haloacid dehalogenase. P6.9 is also encoded by a core gene ( ac100 ) and is required for viral genome encapsidation. It has been reported that multiple phosphorylated species of P6.9 are present in virus-infected cells, while only an unphosphorylated species is detected in the budded virus. Therefore, whether 38K mediates the dephosphorylation of P6.9 was investigated. An additional phosphorylated species of P6.9 in 38K -deleted or -mutated virus-transfected cells was detected, and the dephosphorylated sites mediated by 38K were determined by mass spectrometry. To assess the effects of dephosphorylation of P6.9 mediated by 38K on virus replication, these sites were mutated to glutamic acids (phosphorylation-mimic mutant) or to alanines (phosphorylation-deficient mutant). Studies showed that the nucleocapsid assembly was interrupted in phosphorylation-mimic mutant virus-transfected cells. Taken together, our findings demonstrate that 38K mediates the dephosphorylation of specific sites at the C terminus of P6.9, which is essential for viral genome encapsidation. IMPORTANCE Genome packaging is a fundamental process in the virus life cycle, and viruses have different strategies to perform this step. For several double-stranded DNA (dsDNA) viruses, the procapsid is formed before genome encapsidation, which may require basic proteins that help to neutralize the nucleic acid charge repulsion to facilitate the compaction of the genome within the confined capsid space. Baculovirus encodes a small basic protein, P6.9, which is required for a variety of processes in the virus infection cycle. The phosphorylation of P6.9 is thought to result in nucleocapsid uncoating, while the dephosphorylation of P6.9 is involved in viral DNA encapsidation during nucleocapsid assembly. Here, we demonstrate that a haloacid dehalogenase homolog encoded by baculovirus core gene 38K is involved in nucleocapsid assembly by mediating the dephosphorylation of 5 specific sites at the C terminus of P6.9. This finding contributes to the understanding of the mechanisms of virus nucleocapsid assembly. Copyright © 2018 Lai et al.

The 38K-Mediated Specific Dephosphorylation of the Viral Core Protein P6.9 Plays an Important Role in the Nucleocapsid Assembly of Autographa californica Multiple Nucleopolyhedrovirus

PubMed Central

Lai, Qingying; Li, Ao; Wang, Wei; Yuan, Meijin

2018-01-01

ABSTRACT Encapsidation of the viral genomes, leading to the assembly of the nucleocapsids to form infectious progeny virions, is a key step in many virus life cycles. Baculovirus nucleocapsid assembly is a complex process that involves many proteins. Our previous studies showed that the deletion of the core gene 38K (ac98) interrupted the nucleocapsid assembly by producing capsid sheaths devoid of viral genomes by an unknown mechanism. All homologs of 38K contain conserved motifs of the haloacid dehalogenase superfamily, which are involved in phosphoryl transfer. The requirements of these motifs for nucleocapsid assembly, confirmed in the present study, suggest that 38K may be a functioning haloacid dehalogenase. P6.9 is also encoded by a core gene (ac100) and is required for viral genome encapsidation. It has been reported that multiple phosphorylated species of P6.9 are present in virus-infected cells, while only an unphosphorylated species is detected in the budded virus. Therefore, whether 38K mediates the dephosphorylation of P6.9 was investigated. An additional phosphorylated species of P6.9 in 38K-deleted or -mutated virus-transfected cells was detected, and the dephosphorylated sites mediated by 38K were determined by mass spectrometry. To assess the effects of dephosphorylation of P6.9 mediated by 38K on virus replication, these sites were mutated to glutamic acids (phosphorylation-mimic mutant) or to alanines (phosphorylation-deficient mutant). Studies showed that the nucleocapsid assembly was interrupted in phosphorylation-mimic mutant virus-transfected cells. Taken together, our findings demonstrate that 38K mediates the dephosphorylation of specific sites at the C terminus of P6.9, which is essential for viral genome encapsidation. IMPORTANCE Genome packaging is a fundamental process in the virus life cycle, and viruses have different strategies to perform this step. For several double-stranded DNA (dsDNA) viruses, the procapsid is formed before genome encapsidation, which may require basic proteins that help to neutralize the nucleic acid charge repulsion to facilitate the compaction of the genome within the confined capsid space. Baculovirus encodes a small basic protein, P6.9, which is required for a variety of processes in the virus infection cycle. The phosphorylation of P6.9 is thought to result in nucleocapsid uncoating, while the dephosphorylation of P6.9 is involved in viral DNA encapsidation during nucleocapsid assembly. Here, we demonstrate that a haloacid dehalogenase homolog encoded by baculovirus core gene 38K is involved in nucleocapsid assembly by mediating the dephosphorylation of 5 specific sites at the C terminus of P6.9. This finding contributes to the understanding of the mechanisms of virus nucleocapsid assembly. PMID:29444944

Lipase mediated synthesis of rutin fatty ester: Study of its process parameters and solvent polarity.

PubMed

Vaisali, C; Belur, Prasanna D; Regupathi, Iyyaswami

2017-10-01

Lipophilization of antioxidants is recognized as an effective strategy to enhance solubility and thus effectiveness in lipid based food. In this study, an effort was made to optimize rutin fatty ester synthesis in two different solvent systems to understand the influence of reaction system hydrophobicity on the optimum conditions using immobilised Candida antartica lipase. Under unoptimized conditions, 52.14% and 13.02% conversion was achieved in acetone and tert-butanol solvent systems, respectively. Among all the process parameters, water activity of the system was found to show highest influence on the conversion in each reaction system. In the presence of molecular sieves, the ester production increased to 62.9% in tert-butanol system, unlike acetone system. Under optimal conditions, conversion increased to 60.74% and 65.73% in acetone and tert-butanol system, respectively. This study shows, maintaining optimal water activity is crucial in reaction systems having polar solvents compared to more non-polar solvents. Copyright © 2017 Elsevier Ltd. All rights reserved.

Impact of solvent granularity and layering on tracer hydrodynamics in confinement.

PubMed

Bollinger, Jonathan A; Carmer, James; Jain, Avni; Truskett, Thomas M

2016-11-28

Classic hydrodynamic arguments establish that when a spherical tracer particle is suspended between parallel walls, tracer-wall coupling mediated by the solvent will cause the tracer to exhibit position-dependent diffusivity. We investigate how the diffusivity profiles of confined tracers are impacted by the diameter size-ratio of the tracer to solvent: starting from the classic limit of infinite size-ratio (i.e., continuum solvent), we consider size-ratios of four or less to examine how hydrodynamic predictions are disrupted for systems where the tracer and solvent are of similar scale. We use computer simulations and techniques based on the Fokker-Planck formalism to calculate the diffusivity profiles of hard-sphere tracer particles in hard-sphere solvents, focusing on the dynamics perpendicular to the walls. Given wall separations of several tracer diameters, we first consider confinement between hard walls, where anisotropic structuring at the solvent lengthscale generates inhomogeneity in the tracer free-energy landscape and undermines hydrodynamic predictions locally. We then introduce confining planes that we term transparent walls, which restrict tracer and solvent center-accessibilities while completely eliminating static anisotropy, and reveal position-dependent signatures in tracer diffusivity solely attributable to confinement. With or without suppressing static heterogeneity, we find that tracer diffusivity increasingly deviates on a local basis from hydrodynamic predictions at smaller size-ratios. However, hydrodynamic theory still approximately captures spatially-averaged dynamics across the pores even for very small tracer-solvent size-ratios over a wide range of solvent densities and wall separations.

YB-1 regulates tiRNA-induced Stress Granule formation but not translational repression

PubMed Central

Lyons, Shawn M.; Achorn, Chris; Kedersha, Nancy L.; Anderson, Paul J.; Ivanov, Pavel

2016-01-01

Stress-induced angiogenin (ANG)-mediated tRNA cleavage promotes a cascade of cellular events that starts with production of tRNA-derived stress-induced RNAs (tiRNAs) and culminates with enhanced cell survival. This stress response program relies on a subset tiRNAs that inhibit translation initiation and induce the assembly of stress granules (SGs), cytoplasmic ribonucleoprotein complexes with cytoprotective and pro-survival properties. SG-promoting tiRNAs bear oligoguanine motifs at their 5′-ends, assemble G-quadruplex-like structures and interact with the translational silencer YB-1. We used CRISPR/Cas9-based genetic manipulations and biochemical approaches to examine the role of YB-1 in tiRNA-mediated translational repression and SG assembly. We found that YB-1 directly binds to tiRNAs via its cold shock domain. This interaction is required for packaging of tiRNA-repressed mRNAs into SGs but is dispensable for tiRNA-mediated translational repression. Our studies reveal the functional role of YB-1 in the ANG-mediated stress response program. PMID:27174937

Dimethyl Sulfoxide Protects Escherichia coli from Rapid Antimicrobial-Mediated Killing

PubMed Central

Mi, Hongfei; Wang, Dai; Xue, Yunxin; Zhang, Zhi; Hong, Yuzhi; Drlica, Karl

2016-01-01

The contribution of reactive oxygen species (ROS) to antimicrobial lethality was examined by treating Escherichia coli with dimethyl sulfoxide (DMSO), an antioxidant solvent frequently used in antimicrobial studies. DMSO inhibited killing by ampicillin, kanamycin, and two quinolones and had little effect on MICs. DMSO-mediated protection correlated with decreased ROS accumulation and provided evidence for ROS-mediated programmed cell death. These data support the contribution of ROS to antimicrobial lethality and suggest caution when using DMSO-dissolved antimicrobials for short-time killing assays. PMID:27246776

Structural variations in terbium(III) complexes with 1,3-adamantanedicarboxylate and diverse co-ligands

NASA Astrophysics Data System (ADS)

Thuéry, Pierre

2015-07-01

Terbium nitrate was reacted with 1,3-adamantanedicarboxylic acid (LH2) under solvo-hydrothermal conditions with either N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMA) as organic solvents. Hydrolysation of the latter co-solvents resulted in the formation of formate or acetate ions, which are present as co-ligands in the 1D coordination polymer [Tb(L)(HCOO)(H2O)2] (1) and the 2D assembly [Tb(L)(CH3COO)(H2O)] (2). The increase in dimensionality in the latter arises from the higher connectivity provided by acetate versus formate, the L2- ligand being bis-chelating in both cases. The complex [Tb2(L)3(H2O)5][Tb2(L)3(H2O)4]·3H2O (3), another 1D species, crystallizes alongside crystals of 2. Further addition of cucurbit[6]uril (CB6), with DMF as co-solvent, gave the two complexes [Tb2(L)2(CB6)(H2O)6](NO3)2·6H2O (4) and [H2NMe2]2[Tb(L)(HCOO)2]2·CB6·3H2O (5). Complex 4 crystallizes as a 3D framework in which Tb(L)+ chains are connected by tetradentate CB6 molecules, while 5 unites a carboxylate-bridged anionic 2D planar assembly and layers of CB6 molecules with counter-cations held at both portals.

Rapid ordering of block copolymer thin films

DOE PAGES

Majewski, Pawel W.; Yager, Kevin G.

2016-08-18

Block-copolymers self-assemble into diverse morphologies, where nanoscale order can be finely tuned via block architecture and processing conditions. However, the ultimate usage of these materials in real-world applications may be hampered by the extremely long thermal annealing times—hours or days—required to achieve good order. Here, we provide an overview of the fundamentals of block-copolymer self-assembly kinetics, and review the techniques that have been demonstrated to influence, and enhance, these ordering kinetics. We discuss the inherent tradeoffs between oven annealing, solvent annealing, microwave annealing, zone annealing, and other directed self-assembly methods; including an assessment of spatial and temporal characteristics. Here, wemore » also review both real-space and reciprocal-space analysis techniques for quantifying order in these systems.« less

The LINKS motif zippers trans-acyltransferase polyketide synthase assembly lines into a biosynthetic megacomplex.

PubMed

Gay, Darren C; Wagner, Drew T; Meinke, Jessica L; Zogzas, Charles E; Gay, Glen R; Keatinge-Clay, Adrian T

2016-03-01

Polyketides such as the clinically-valuable antibacterial agent mupirocin are constructed by architecturally-sophisticated assembly lines known as trans-acyltransferase polyketide synthases. Organelle-sized megacomplexes composed of several copies of trans-acyltransferase polyketide synthase assembly lines have been observed by others through transmission electron microscopy to be located at the Bacillus subtilis plasma membrane, where the synthesis and export of the antibacterial polyketide bacillaene takes place. In this work we analyze ten crystal structures of trans-acyltransferase polyketide synthases ketosynthase domains, seven of which are reported here for the first time, to characterize a motif capable of zippering assembly lines into a megacomplex. While each of the three-helix LINKS (Laterally-INteracting Ketosynthase Sequence) motifs is observed to similarly dock with a spatially-reversed copy of itself through hydrophobic and ionic interactions, the amino acid sequences of this motif are not conserved. Such a code is appropriate for mediating homotypic contacts between assembly lines to ensure the ordered self-assembly of a noncovalent, yet tightly-knit, enzymatic network. LINKS-mediated lateral interactions would also have the effect of bolstering the vertical association of the polypeptides that comprise a polyketide synthase assembly line. Copyright © 2015 Elsevier Inc. All rights reserved.

The LINKS motif zippers trans-acyltransferase polyketide synthase assembly lines into a biosynthetic megacomplex

PubMed Central

Gay, Darren C.; Wagner, Drew T.; Meinke, Jessica L.; Zogzas, Charles E.; Gay, Glen R.; Keatinge-Clay, Adrian T.

2016-01-01

Polyketides such as the clinically-valuable antibacterial agent mupirocin are constructed by architecturally-sophisticated assembly lines known as trans-acyltransferase polyketide synthases. Organelle-sized megacomplexes composed of several copies of trans-acyltransferase polyketide synthase assembly lines have been observed by others through transmission electron microscopy to be located at the Bacillus subtilis plasma membrane, where the synthesis and export of the antibacterial polyketide bacillaene takes place. In this work we analyze ten crystal structures of trans-acyltransferase polyketide synthases ketosynthase domains, seven of which are reported here for the first time, to characterize a motif capable of zippering assembly lines into a megacomplex. While each of the three-helix LINKS (Laterally-INteracting Ketosynthase Sequence) motifs is observed to similarly dock with a spatially-reversed copy of itself through hydrophobic and ionic interactions, the amino acid sequences of this motif are not conserved. Such a code is appropriate for mediating homotypic contacts between assembly lines to ensure the ordered self-assembly of a noncovalent, yet tightly-knit, enzymatic network. LINKS-mediated lateral interactions would also have the effect of bolstering the vertical association of the polypeptides that comprise a polyketide synthase assembly line. PMID:26724270

Selective regulation of clathrin-mediated epidermal growth factor receptor signaling and endocytosis by phospholipase C and calcium

PubMed Central

Delos Santos, Ralph Christian; Bautista, Stephen; Lucarelli, Stefanie; Bone, Leslie N.; Dayam, Roya M.; Abousawan, John; Botelho, Roberto J.; Antonescu, Costin N.

2017-01-01

Clathrin-mediated endocytosis is a major regulator of cell-surface protein internalization. Clathrin and other proteins assemble into small invaginating structures at the plasma membrane termed clathrin-coated pits (CCPs) that mediate vesicle formation. In addition, epidermal growth factor receptor (EGFR) signaling is regulated by its accumulation within CCPs. Given the diversity of proteins regulated by clathrin-mediated endocytosis, how this process may distinctly regulate specific receptors is a key question. We examined the selective regulation of clathrin-dependent EGFR signaling and endocytosis. We find that perturbations of phospholipase Cγ1 (PLCγ1), Ca2+, or protein kinase C (PKC) impair clathrin-mediated endocytosis of EGFR, the formation of CCPs harboring EGFR, and EGFR signaling. Each of these manipulations was without effect on the clathrin-mediated endocytosis of transferrin receptor (TfR). EGFR and TfR were recruited to largely distinct clathrin structures. In addition to control of initiation and assembly of CCPs, EGF stimulation also elicited a Ca2+- and PKC-dependent reduction in synaptojanin1 recruitment to clathrin structures, indicating broad control of CCP assembly by Ca2+ signals. Hence EGFR elicits PLCγ1-calcium signals to facilitate formation of a subset of CCPs, thus modulating its own signaling and endocytosis. This provides evidence for the versatility of CCPs to control diverse cellular processes. PMID:28814502

Elucidating the role of methyl viologen as a scavenger of photoactivated electrons from photosystem I under aerobic and anaerobic conditions.

PubMed

Bennett, Tyler; Niroomand, Hanieh; Pamu, Ravi; Ivanov, Ilia; Mukherjee, Dibyendu; Khomami, Bamin

2016-03-28

We present detailed electrochemical investigations into the role of dissolved O2 in electrolyte solutions in scavenging photoactivated electrons from a uniform photosystem I (PS I) monolayer assembled on alkanethiolate SAM (self-assembled monolayer)/Au surfaces while using methyl viologen (MV(2+)) as the redox mediator. To this end, we report results for direct measurements of light induced photocurrent from uniform monolayer assemblies of PS I on C9 alkanethiolate SAM/Au surfaces. These measurements, apart from demonstrating the ability of dissolved O2 in the electrolyte medium to act as an electron scavenger, also reveal its essential role in driving the solution-phase methyl viologen to initiate light-induced directional electron transfer from an electron donor surface (Au) via surface assembled PS I trimers. Specifically, our systematic electrochemical measurements have revealed that the dissolved O2 in aqueous electrolyte solutions form a complex intermediate species with MV that plays the essential role in mediating redox pathways for unidirectional electron transfer processes. This critical insight into the redox-mediated electron transfer pathways allows for rational design of electron scavengers through systematic tuning of mediator combinations that promote such intermediate formation. Our current findings facilitate the incorporation of PS I-based bio-hybrid constructs as photo-anodes in future photoelectrochemical cells and bio-electronic devices.

Transcription regulation by the Mediator complex.

PubMed

Soutourina, Julie

2018-04-01

Alterations in the regulation of gene expression are frequently associated with developmental diseases or cancer. Transcription activation is a key phenomenon in the regulation of gene expression. In all eukaryotes, mediator of RNA polymerase II transcription (Mediator), a large complex with modular organization, is generally required for transcription by RNA polymerase II, and it regulates various steps of this process. The main function of Mediator is to transduce signals from the transcription activators bound to enhancer regions to the transcription machinery, which is assembled at promoters as the preinitiation complex (PIC) to control transcription initiation. Recent functional studies of Mediator with the use of structural biology approaches and functional genomics have revealed new insights into Mediator activity and its regulation during transcription initiation, including how Mediator is recruited to transcription regulatory regions and how it interacts and cooperates with PIC components to assist in PIC assembly. Novel roles of Mediator in the control of gene expression have also been revealed by showing its connection to the nuclear pore and linking Mediator to the regulation of gene positioning in the nuclear space. Clear links between Mediator subunits and disease have also encouraged studies to explore targeting of this complex as a potential therapeutic approach in cancer and fungal infections.

Mediator binds to boundaries of chromosomal interaction domains and to proteins involved in DNA looping, RNA metabolism, chromatin remodeling, and actin assembly

PubMed Central

Chereji, Răzvan V.; Bharatula, Vasudha; Elfving, Nils; Blomberg, Jeanette; Larsson, Miriam; Morozov, Alexandre V.; Broach, James R.

2017-01-01

Abstract Mediator is a multi-unit molecular complex that plays a key role in transferring signals from transcriptional regulators to RNA polymerase II in eukaryotes. We have combined biochemical purification of the Saccharomyces cerevisiae Mediator from chromatin with chromatin immunoprecipitation in order to reveal Mediator occupancy on DNA genome-wide, and to identify proteins interacting specifically with Mediator on the chromatin template. Tandem mass spectrometry of proteins in immunoprecipitates of mediator complexes revealed specific interactions between Mediator and the RSC, Arp2/Arp3, CPF, CF 1A and Lsm complexes in chromatin. These factors are primarily involved in chromatin remodeling, actin assembly, mRNA 3′-end processing, gene looping and mRNA decay, but they have also been shown to enter the nucleus and participate in Pol II transcription. Moreover, we have found that Mediator, in addition to binding Pol II promoters, occupies chromosomal interacting domain (CID) boundaries and that Mediator in chromatin associates with proteins that have been shown to interact with CID boundaries, such as Sth1, Ssu72 and histone H4. This suggests that Mediator plays a significant role in higher-order genome organization. PMID:28575439

Multiple electrokinetic actuators for feedback control of colloidal crystal size.

PubMed

Juárez, Jaime J; Mathai, Pramod P; Liddle, J Alexander; Bevan, Michael A

2012-10-21

We report a feedback control method to precisely target the number of colloidal particles in quasi-2D ensembles and their subsequent assembly into crystals in a quadrupole electrode. Our approach relies on tracking the number of particles within a quadrupole electrode, which is used in a real-time feedback control algorithm to dynamically actuate competing electrokinetic transport mechanisms. Particles are removed from the quadrupole using DC-field mediated electrophoretic-electroosmotic transport, while high-frequency AC-field mediated dielectrophoretic transport is used to concentrate and assemble colloidal crystals. Our results show successful control of the size of crystals containing 20 to 250 colloidal particles with less than 10% error. Assembled crystals are characterized by their radius of gyration, crystallinity, and number of edge particles, and demonstrate the expected size-dependent properties. Our findings demonstrate successful ensemble feedback control of the assembly of different sized colloidal crystals using multiple actuators, which has broad implications for control over nano- and micro- scale assembly processes involving colloidal components.

Stepwise self-assembly of C60 mediated by atomic scale moiré magnifiers

NASA Astrophysics Data System (ADS)

Gruznev, D. V.; Matetskiy, A. V.; Bondarenko, L. V.; Utas, O. A.; Zotov, A. V.; Saranin, A. A.; Chou, J. P.; Wei, C. M.; Lai, M. Y.; Wang, Y. L.

2013-04-01

Self-assembly of atoms or molecules on a crystal surface is considered one of the most promising methods to create molecular devices. Here we report a stepwise self-assembly of C60 molecules into islands with unusual shapes and preferred sizes on a gold-indium-covered Si(111) surface. Specifically, 19-mer islands prefer a non-compact boomerang shape, whereas hexagonal 37-mer islands exhibit extraordinarily enhanced stability and abundance. The stepwise self-assembly is mediated by the moiré interference between an island with its underlying lattice, which essentially maps out the adsorption-energy landscape of a C60 on different positions of the surface with a lateral magnification factor and dictates the probability for the subsequent attachment of C60 to an island’s periphery. Our discovery suggests a new method for exploiting the moiré interference to dynamically assist the self-assembly of particles and provides an unexplored tactic of engineering atomic scale moiré magnifiers to facilitate the growth of monodispersed mesoscopic structures.

Phosphorylation on Ser-279 and Ser-282 of connexin43 regulates endocytosis and gap junction assembly in pancreatic cancer cells

PubMed Central

Johnson, Kristen E.; Mitra, Shalini; Katoch, Parul; Kelsey, Linda S.; Johnson, Keith R.; Mehta, Parmender P.

2013-01-01

The molecular mechanisms regulating the assembly of connexins (Cxs) into gap junctions are poorly understood. Using human pancreatic tumor cell lines BxPC3 and Capan-1, which express Cx26 and Cx43, we show that, upon arrival at the cell surface, the assembly of Cx43 is impaired. Connexin43 fails to assemble, because it is internalized by clathrin-mediated endocytosis. Assembly is restored upon expressing a sorting-motif mutant of Cx43, which does not interact with the AP2 complex, and by expressing mutants that cannot be phosphorylated on Ser-279 and Ser-282. The mutants restore assembly by preventing clathrin-mediated endocytosis of Cx43. Our results also document that the sorting-motif mutant is assembled into gap junctions in cells in which the expression of endogenous Cx43 has been knocked down. Remarkably, Cx43 mutants that cannot be phosphorylated on Ser-279 or Ser-282 are assembled into gap junctions only when connexons are composed of Cx43 forms that can be phosphorylated on these serines and forms in which phosphorylation on these serines is abolished. Based on the subcellular fate of Cx43 in single and contacting cells, our results document that the endocytic itinerary of Cx43 is altered upon cell–cell contact, which causes Cx43 to traffic by EEA1-negative endosomes en route to lysosomes. Our results further show that gap-junctional plaques formed of a sorting motif–deficient mutant of Cx43, which is unable to be internalized by the clathrin-mediated pathway, are predominantly endocytosed in the form of annular junctions. Thus the differential phosphorylation of Cx43 on Ser-279 and Ser-282 is fine-tuned to control Cx43’s endocytosis and assembly into gap junctions. PMID:23363606

Molecular Architecture of the Human Mediator–RNA Polymerase II–TFIIF Assembly

PubMed Central

Bernecky, Carrie; Grob, Patricia; Ebmeier, Christopher C.; Nogales, Eva; Taatjes, Dylan J.

2011-01-01

The macromolecular assembly required to initiate transcription of protein-coding genes, known as the Pre-Initiation Complex (PIC), consists of multiple protein complexes and is approximately 3.5 MDa in size. At the heart of this assembly is the Mediator complex, which helps regulate PIC activity and interacts with the RNA polymerase II (pol II) enzyme. The structure of the human Mediator–pol II interface is not well-characterized, whereas attempts to structurally define the Mediator–pol II interaction in yeast have relied on incomplete assemblies of Mediator and/or pol II and have yielded inconsistent interpretations. We have assembled the complete, 1.9 MDa human Mediator–pol II–TFIIF complex from purified components and have characterized its structural organization using cryo-electron microscopy and single-particle reconstruction techniques. The orientation of pol II within this assembly was determined by crystal structure docking and further validated with projection matching experiments, allowing the structural organization of the entire human PIC to be envisioned. Significantly, pol II orientation within the Mediator–pol II–TFIIF assembly can be reconciled with past studies that determined the location of other PIC components relative to pol II itself. Pol II surfaces required for interacting with TFIIB, TFIIE, and promoter DNA (i.e., the pol II cleft) are exposed within the Mediator–pol II–TFIIF structure; RNA exit is unhindered along the RPB4/7 subunits; upstream and downstream DNA is accessible for binding additional factors; and no major structural re-organization is necessary to accommodate the large, multi-subunit TFIIH or TFIID complexes. The data also reveal how pol II binding excludes Mediator–CDK8 subcomplex interactions and provide a structural basis for Mediator-dependent control of PIC assembly and function. Finally, parallel structural analysis of Mediator–pol II complexes lacking TFIIF reveal that TFIIF plays a key role in stabilizing pol II orientation within the assembly. PMID:21468301

Nanoscale silicon substrate patterns from self-assembly of cylinder forming poly(styrene)-block-poly(dimethylsiloxane) block copolymer on silane functionalized surfaces.

PubMed

Borah, Dipu; Cummins, Cian; Rasappa, Sozaraj; Watson, Scott M D; Pike, Andrew R; Horrocks, Benjamin R; Fulton, David A; Houlton, Andrew; Liontos, George; Ntetsikas, Konstantinos; Avgeropoulos, Apostolos; Morris, Michael A

2017-01-27

Poly(styrene)-block-poly(dimethylsiloxane) (PS-b-PDMS) is an excellent block copolymer (BCP) system for self-assembly and inorganic template fabrication because of its high Flory-Huggins parameter (χ ∼ 0.26) at room temperature in comparison to other BCPs, and high selective etch contrast between PS and PDMS block for nanopatterning. In this work, self-assembly in PS-b-PDMS BCP is achieved by combining hydroxyl-terminated poly(dimethylsiloxane) (PDMS-OH) brush surfaces with solvent vapor annealing. As an alternative to standard brush chemistry, we report a simple method based on the use of surfaces functionalized with silane-based self-assembled monolayers (SAMs). A solution-based approach to SAM formation was adopted in this investigation. The influence of the SAM-modified surfaces upon BCP films was compared with polymer brush-based surfaces. The cylinder forming PS-b-PDMS BCP and PDMS-OH polymer brush were synthesized by sequential living anionic polymerization. It was observed that silane SAMs provided the appropriate surface chemistry which, when combined with solvent annealing, led to microphase segregation in the BCP. It was also demonstrated that orientation of the PDMS cylinders may be controlled by judicious choice of the appropriate silane. The PDMS patterns were successfully used as an on-chip etch mask to transfer the BCP pattern to underlying silicon substrate with sub-25 nm silicon nanoscale features. This alternative SAM/BCP approach to nanopattern formation shows promising results, pertinent in the field of nanotechnology, and with much potential for application, such as in the fabrication of nanoimprint lithography stamps, nanofluidic devices or in narrow and multilevel interconnected lines.

Nanoscale silicon substrate patterns from self-assembly of cylinder forming poly(styrene)-block-poly(dimethylsiloxane) block copolymer on silane functionalized surfaces

NASA Astrophysics Data System (ADS)

Borah, Dipu; Cummins, Cian; Rasappa, Sozaraj; Watson, Scott M. D.; Pike, Andrew R.; Horrocks, Benjamin R.; Fulton, David A.; Houlton, Andrew; Liontos, George; Ntetsikas, Konstantinos; Avgeropoulos, Apostolos; Morris, Michael A.

2017-01-01

Poly(styrene)-block-poly(dimethylsiloxane) (PS-b-PDMS) is an excellent block copolymer (BCP) system for self-assembly and inorganic template fabrication because of its high Flory-Huggins parameter (χ ˜ 0.26) at room temperature in comparison to other BCPs, and high selective etch contrast between PS and PDMS block for nanopatterning. In this work, self-assembly in PS-b-PDMS BCP is achieved by combining hydroxyl-terminated poly(dimethylsiloxane) (PDMS-OH) brush surfaces with solvent vapor annealing. As an alternative to standard brush chemistry, we report a simple method based on the use of surfaces functionalized with silane-based self-assembled monolayers (SAMs). A solution-based approach to SAM formation was adopted in this investigation. The influence of the SAM-modified surfaces upon BCP films was compared with polymer brush-based surfaces. The cylinder forming PS-b-PDMS BCP and PDMS-OH polymer brush were synthesized by sequential living anionic polymerization. It was observed that silane SAMs provided the appropriate surface chemistry which, when combined with solvent annealing, led to microphase segregation in the BCP. It was also demonstrated that orientation of the PDMS cylinders may be controlled by judicious choice of the appropriate silane. The PDMS patterns were successfully used as an on-chip etch mask to transfer the BCP pattern to underlying silicon substrate with sub-25 nm silicon nanoscale features. This alternative SAM/BCP approach to nanopattern formation shows promising results, pertinent in the field of nanotechnology, and with much potential for application, such as in the fabrication of nanoimprint lithography stamps, nanofluidic devices or in narrow and multilevel interconnected lines.

Phosphorylation of Nephrin Triggers Its Internalization by Raft-Mediated Endocytosis

PubMed Central

Qin, Xiao-Song; Shono, Akemi; Yamamoto, Akitsugu; Kurihara, Hidetake; Doi, Toshio

2009-01-01

Proper localization of nephrin determines integrity of the glomerular slit diaphragm. Slit diaphragm proteins assemble into functional signaling complexes on a raft-based platform, but how the trafficking of these proteins coordinates with their signaling function is unknown. Here, we demonstrate that a raft-mediated endocytic (RME) pathway internalizes nephrin. Nephrin internalization was slower with raft-mediated endocytosis than with classic clathrin-mediated endocytosis. Ultrastructurally, the RME pathway consisted of noncoated invaginations and was dependent on cholesterol and dynamin. Nephrin constituted a stable, signaling-competent microdomain through interaction with Fyn, a Src kinase, and podocin, a scaffold protein. Tyrosine phosphorylation of nephrin triggered its own RME-mediated internalization. Protamine-induced hyperphosphorylation of nephrin led to noncoated invaginations predominating over coated pits. These results demonstrate that an RME pathway couples nephrin internalization to its own signaling, suggesting that RME promotes proper spatiotemporal assembly of slit diaphragms during podocyte development or injury. PMID:19850954

A Collapsin Response Mediator Protein 2 Isoform Controls Myosin II-Mediated Cell Migration and Matrix Assembly by Trapping ROCK II

PubMed Central

Morgan-Fisher, Marie; Wait, Robin; Couchman, John R.; Wewer, Ulla M.

2012-01-01

Collapsin response mediator protein 2 (CRMP-2) is known as a regulator of neuronal polarity and differentiation through microtubule assembly and trafficking. Here, we show that CRMP-2 is ubiquitously expressed and a splice variant (CRMP-2L), which is expressed mainly in epithelial cells among nonneuronal cells, regulates myosin II-mediated cellular functions, including cell migration. While the CRMP-2 short form (CRMP-2S) is recognized as a substrate of the Rho-GTP downstream kinase ROCK in neuronal cells, a CRMP-2 complex containing 2L not only bound the catalytic domain of ROCK II through two binding domains but also trapped and inhibited the kinase. CRMP-2L protein levels profoundly affected haptotactic migration and the actin-myosin cytoskeleton of carcinoma cells as well as nontransformed epithelial cell migration in a ROCK activity-dependent manner. Moreover, the ectopic expression of CRMP-2L but not -2S inhibited fibronectin matrix assembly in fibroblasts. Underlying these responses, CRMP-2L regulated the kinase activity of ROCK II but not ROCK I, independent of GTP-RhoA levels. This study provides a new insight into CRMP-2 as a controller of myosin II-mediated cellular functions through the inhibition of ROCK II in nonneuronal cells. PMID:22431514

The Dimanganese(II) Site of Bacillus subtilis Class Ib Ribonucleotide Reductase

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boal, Amie K.; Cotruvo, Jr., Joseph A.; Stubbe, JoAnne

2014-10-02

Class Ib ribonucleotide reductases (RNRs) use a dimanganese-tyrosyl radical cofactor, Mn{sub 2}{sup III}-Y{sm_bullet}, in their homodimeric NrdF ({beta}2) subunit to initiate reduction of ribonucleotides to deoxyribonucleotides. The structure of the Mn{sub 2}{sup II} form of NrdF is an important component in understanding O{sub 2}-mediated formation of the active metallocofactor, a subject of much interest because a unique flavodoxin, NrdI, is required for cofactor assembly. Biochemical studies and sequence alignments suggest that NrdF and NrdI proteins diverge into three phylogenetically distinct groups. The only crystal structure to date of a NrdF with a fully ordered and occupied dimanganese site is thatmore » of Escherichia coli Mn{sub 2}{sup II}-NrdF, prototypical of the enzymes from actinobacteria and proteobacteria. Here we report the 1.9 {angstrom} resolution crystal structure of Bacillus subtilis Mn{sub 2}{sup II}-NrdF, representative of the enzymes from a second group, from Bacillus and Staphylococcus. The structures of the metal clusters in the {beta}2 dimer are distinct from those observed in E. coli Mn{sub 2}{sup II}-NrdF. These differences illustrate the key role that solvent molecules and protein residues in the second coordination sphere of the Mn{sub 2}{sup II} cluster play in determining conformations of carboxylate residues at the metal sites and demonstrate that diverse coordination geometries are capable of serving as starting points for Mn{sub 2}{sup III}-Y{sm_bullet} cofactor assembly in class Ib RNRs.« less

Approaches to efficiently estimate solvation and explicit water energetics in ligand binding: the use of WaterMap [WaterMap and Its Implementation in Drug Discovery

DOE PAGES

Yang, Yue; Wong, Sergio E.; Lightstone, Felice C.

2012-09-08

Solvents play quite an important role in most chemical and biological processes. It is widely accepted that the presence of water or other solvents in many chemical reactions can result in much lower energy barrier. In enzymatic catalysis, water mediated reaction pathways have been observed in various studies. In addition, different conformation flexibility and hydrogen bond patterns have been discovered for cyclic peptides in the presence of membrane and water, further illustrating the impact of solvent in biological activities such like membrane penetration. moreover, as will be discussed later in this review, water also plays a critical role in host-guestmore » chemistry and thus is essential to drug design. As such, it is not surprising that accounting for solvents is critical in drug discovery since drugs must modulate biological systems.« less

Clean Transfer of Wafer-Scale Graphene via Liquid Phase Removal of Polycyclic Aromatic Hydrocarbons.

PubMed

Kim, Hyun Ho; Kang, Boseok; Suk, Ji Won; Li, Nannan; Kim, Kwang S; Ruoff, Rodney S; Lee, Wi Hyoung; Cho, Kilwon

2015-05-26

Pentacene (C22H14), a polycyclic aromatic hydrocarbon, was used as both supporting and sacrificing layers for the clean and doping-free graphene transfer. After successful transfer of graphene to a target substrate, the pentacene layer was physically removed from the graphene surface by using intercalating organic solvent. This solvent-mediated removal of pentacene from graphene surface was investigated by both theoretical calculation and experimental studies with various solvents. The uses of pentacene and appropriate intercalation solvent enabled graphene transfer without forming a residue from the supporting layer. Such residues tend to cause charged impurity scattering and unintentional graphene doping effects. As a result, this clean graphene exhibited extremely homogeneous surface potential profiles over a large area. A field-effect transistor fabricated using this graphene displayed a high hole (electron) mobility of 8050 cm(2)/V·s (9940 cm(2)/V·s) with a nearly zero Dirac point voltage.

Study on the Preparation Process and Influential Factors of Large Area Environment-friendly Molten Carbonate Fuel Cell Matrix

NASA Astrophysics Data System (ADS)

Zhang, Ruiyun; Xu, Shisen; Cheng, Jian; Wang, Hongjian; Ren, Yongqiang

2017-07-01

Low-cost and high-performance matrix materials used in mass production of molten carbonate fuel cell (MCFC) were prepared by automatic casting machine with α-LiAlO2 powder material synthesized by gel-solid method, and distilled water as solvent. The single cell was assembled for generating test, and the good performance of the matrix was verified. The paper analyzed the factors affecting aqueous tape casting matrix preparation, such as solvent content, dispersant content, milling time, blade height and casting machine running speed, providing a solid basis for the mass production of large area environment-friendly matrix used in molten carbonate fuel cell.

Solvent-mediated nonelectrostatic ion-ion interactions predicting anomalies in electrophoresis.

PubMed

Goswami, Prakash; Dhar, Jayabrata; Ghosh, Uddipta; Chakraborty, Suman

2017-03-01

We study the effects of solvent-mediated nonelectrostatic ion-ion interactions on electrophoretic mobility of a charged spherical particle. To this end, we consider the case of low surface electrostatic potential resulting in the linearization of the governing equations, which enables us to deduce a closed-form analytical solution to the electrophoretic mobility. We subsequently compare our results to the standard model using Henry's approach and report the changes brought about by the nonelectrostatic potential. The classical approach to determine the electrophoretic mobility underpredicts the particle velocity when compared with experiments. We show that this issue can be resolved by taking into account nonelectrostatic interactions. Our analysis further reveals the phenomenon of electrophoretic mobility reversal that has been experimentally observed in numerous previous studies. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Reversible Self-Assembly of 3D Architectures Actuated by Responsive Polymers.

PubMed

Zhang, Cheng; Su, Jheng-Wun; Deng, Heng; Xie, Yunchao; Yan, Zheng; Lin, Jian

2017-11-29

An assembly of three-dimensional (3D) architectures with defined configurations has important applications in broad areas. Among various approaches of constructing 3D structures, a stress-driven assembly provides the capabilities of creating 3D architectures in a broad range of functional materials with unique merits. However, 3D architectures built via previous methods are simple, irreversible, or not free-standing. Furthermore, the substrates employed for the assembly remain flat, thus not involved as parts of the final 3D architectures. Herein, we report a reversible self-assembly of various free-standing 3D architectures actuated by the self-folding of smart polymer substrates with programmed geometries. The strategically designed polymer substrates can respond to external stimuli, such as organic solvents, to initiate the 3D assembly process and subsequently become the parts of the final 3D architectures. The self-assembly process is highly controllable via origami and kirigami designs patterned by direct laser writing. Self-assembled geometries include 3D architectures such as "flower", "rainbow", "sunglasses", "box", "pyramid", "grating", and "armchair". The reported self-assembly also shows wide applicability to various materials including epoxy, polyimide, laser-induced graphene, and metal films. The device examples include 3D architectures integrated with a micro light-emitting diode and a flex sensor, indicting the potential applications in soft robotics, bioelectronics, microelectromechanical systems, and others.

Triggered and catalyzed self-assembly of hyperbranched DNA structures for logic operations and homogeneous CRET biosensing of microRNA.

PubMed

Bi, Sai; Yue, Shuzhen; Wu, Qiang; Ye, Jiayan

2016-04-07

Toehold-mediated strand displacement-based nanocircuits are developed by integrating catalytic hairpin assembly (CHA) with hybridization chain reaction (HCR), which achieves self-assembly of hyperbranched DNA structures and is readily utilized as an enzyme-free amplifier for homogeneous CRET detection of microRNA with high sensitivity and selectivity.

Structure of the CFA/III major pilin subunit CofA from human enterotoxigenic Escherichia coli determined at 0.90 Å resolution by sulfur-SAD phasing.

PubMed

Fukakusa, Shunsuke; Kawahara, Kazuki; Nakamura, Shota; Iwashita, Takaki; Baba, Seiki; Nishimura, Mitsuhiro; Kobayashi, Yuji; Honda, Takeshi; Iida, Tetsuya; Taniguchi, Tooru; Ohkubo, Tadayasu

2012-10-01

CofA, a major pilin subunit of colonization factor antigen III (CFA/III), forms pili that mediate small-intestinal colonization by enterotoxigenic Escherichia coli (ETEC). In this study, the crystal structure of an N-terminally truncated version of CofA was determined by single-wavelength anomalous diffraction (SAD) phasing using five sulfurs in the protein. Given the counterbalance between anomalous signal strength and the undesired X-ray absorption of the solvent, diffraction data were collected at 1.5 Å resolution using synchrotron radiation. These data were sufficient to elucidate the sulfur substructure at 1.38 Å resolution. The low solvent content (29%) of the crystal necessitated that density modification be performed with an additional 0.9 Å resolution data set to reduce the phase error caused by the small sulfur anomalous signal. The CofA structure showed the αβ-fold typical of type IVb pilins and showed high structural homology to that of TcpA for toxin-coregulated pili of Vibrio cholerae, including spatial distribution of key residues critical for pilin self-assembly. A pilus-filament model of CofA was built by computational docking and molecular-dynamics simulation using the previously reported filament model of TcpA as a structural template. This model revealed that the CofA filament surface was highly negatively charged and that a 23-residue-long loop between the α1 and α2 helices filled the gap between the pilin subunits. These characteristics could provide a unique binding epitope for the CFA/III pili of ETEC compared with other type IVb pili.

Selective DNA-Mediated Assembly of Gold Nanoparticles on Electroded Substrates

DTIC Science & Technology

2008-06-01

might use the Watson - Crick base-pairing of DNA as a means for ultrahigh-precision engineering is well- known.5,6 The idea is to use the highly specific...Selective DNA -Mediated Assembly of Gold Nanoparticles on Electroded Substrates K. E. Sapsford,†,‡,∇ D. Park,§ E. R. Goldman,‡ E. E. Foos,| S. A...electrodes via DNA hybridization. Protocols are demonstrated for maximizing selectivity and coverage using 15mers as the active binding agents. Detailed

Increased microtubule assembly rates mediate chromosomal instability in colorectal cancer cells

PubMed Central

Ertych, Norman; Stolz, Ailine; Stenzinger, Albrecht; Weichert, Wilko; Kaulfuß, Silke; Burfeind, Peter; Aigner, Achim; Wordeman, Linda

2015-01-01

Chromosomal instability (CIN) is defined as the perpetual missegregation of whole chromosomes during mitosis and represents a hallmark of human cancer. However, the mechanisms causing CIN and its consequences on tumor growth are largely unknown. We identify an increase in microtubule plus end assembly rates as a fundamental trigger for CIN in CRC cells. This trigger is mediated by overexpression of the oncogene AURKA or by loss of the tumor suppressor gene CHK2, a genetic constitution found in 73% of human colorectal cancers. Increased microtubule assembly rates are associated with transient abnormalities in mitotic spindle geometry promoting the generation of lagging chromosomes and resulting in CIN. Reconstitution of proper microtubule assembly rates by chemical or genetic means suppresses CIN and thereby, unexpectedly, accelerates tumor growth in vitro and in vivo. Thus, we identify a fundamental mechanism triggering CIN in cancer cells and reveal its adverse consequence on tumor growth. PMID:24976383

Soft-template mediated synthesis of GaOOH nanorod-shelled microspheres and thermal conversion to beta-Ga2O3.

PubMed

Wang, Jian; Li, Qi; Qiu, Xiaohui; He, Yujian; Liu, Wei

2010-07-01

Micrometer-scale hollow spheres self-assembled by GaOOH nanorods were synthesized under hydrothermal conditions using gallium nitrate and sodium hydroxide as starting materials. The structures and morphologies of the products were studied by X-ray diffraction and scanning electron microscopy. Time-dependent experiments revealed three stages involved in the process of reaction including the initial stage of formation of surfactant vesicles which can be considered as soft templates, followed by the nucleation of GaOOH nanoclusters, and the assembling and growth of nanorods under the modulation of the spherical vesicles. The growth kinetics of the GaOOH nanorods was systematically investigated. Based on the experimental observation, a template-mediated assembling mechanism was proposed. We further demonstrated that the GaOOH nanorods could be converted to gallium oxide (beta-Ga2O3) nanorods by calcination without changing the spherical morphology of the assemblies.

Grooved nanowires from self-assembling hairpin molecules for solar cells.

PubMed

Tevis, Ian D; Tsai, Wei-Wen; Palmer, Liam C; Aytun, Taner; Stupp, Samuel I

2012-03-27

One of the challenges facing bulk heterojunction organic solar cells is obtaining organized films during the phase separation of intimately mixed donor and acceptor components. We report here on the use of hairpin-shaped sexithiophene molecules to generate by self-assembly grooved nanowires as the donor component in bulk heterojunction solar cells. Photovoltaic devices were fabricated via spin-casting to produce by solvent evaporation a percolating network of self-assembled nanowires and fullerene acceptors. Thermal annealing was found to increase power conversion efficiencies by promoting domain growth while still maintaining this percolating network of nanostructures. The benefits of self-assembly and grooved nanowires were examined by building devices from a soluble sexithiophene derivative that does not form one-dimensional structures. In these systems, excessive phase separation caused by thermal annealing leads to the formation of defects and lower device efficiencies. We propose that the unique hairpin shape of the self-assembling molecules allows the nanowires as they form to interact well with the fullerenes in receptor-ligand type configurations at the heterojunction of the two domains, thus enhancing device efficiencies by 23%. © 2012 American Chemical Society

Molecular Self-Assembly Strategy for Generating Catalytic Hybrid Polypeptides

PubMed Central

Ikezoe, Yasuhiro; Pike, Douglas H.; Nanda, Vikas; Matsui, Hiroshi

2016-01-01

Recently, catalytic peptides were introduced that mimicked protease activities and showed promising selectivity of products even in organic solvents where protease cannot perform well. However, their catalytic efficiency was extremely low compared to natural enzyme counterparts presumably due to the lack of stable tertiary fold. We hypothesized that assembling these peptides along with simple hydrophobic pockets, mimicking enzyme active sites, could enhance the catalytic activity. Here we fused the sequence of catalytic peptide CP4, capable of protease and esterase-like activities, into a short amyloidogenic peptide fragment of Aβ. When the fused CP4-Aβ construct assembled into antiparallel β-sheets and amyloid fibrils, a 4.0-fold increase in the hydrolysis rate of p-nitrophenyl acetate (p-NPA) compared to neat CP4 peptide was observed. The enhanced catalytic activity of CP4-Aβ assembly could be explained both by pre-organization of a catalytically competent Ser-His-acid triad and hydrophobic stabilization of a bound substrate between the triad and p-NPA, indicating that a design strategy for self-assembled peptides is important to accomplish the desired functionality. PMID:27116246

Molecular self-assembly strategy for generating catalytic hybrid polypeptides

DOE PAGES

Maeda, Yoshiaki; Fang, Justin; Ikezoe, Yasuhiro; ...

2016-04-26

Recently, catalytic peptides were introduced that mimicked protease activities and showed promising selectivity of products even in organic solvents where protease cannot perform well. However, their catalytic efficiency was extremely low compared to natural enzyme counterparts presumably due to the lack of stable tertiary fold. We hypothesized that assembling these peptides along with simple hydrophobic pockets, mimicking enzyme active sites, could enhance the catalytic activity. Here we fused the sequence of catalytic peptide CP4, capable of protease and esterase-like activities, into a short amyloidogenic peptide fragment of Aβ. When the fused CP4-Aβ construct assembled into antiparallel β- sheets and amyloidmore » fibrils, a 4.0-fold increase in the hydrolysis rate of p-nitrophenyl acetate (p-NPA) compared to neat CP4 peptide was observed. Furthermore, the enhanced catalytic activity of CP4-Aβ assembly could be explained both by pre-organization of a catalytically competent Ser-His-acid triad and hydrophobic stabilization of a bound substrate between the triad and p-NPA, indicating that a design strategy for self-assembled peptides is important to accomplish the desired functionality.« less

Self-assembled nanocages based on the coiled coil bundle motif

NASA Astrophysics Data System (ADS)

Sinha, Nairiti; Villegas, Jose; Saven, Jeffery; Kiick, Kristi; Pochan, Darrin

Computational design of coiled coil peptide bundles that undergo solution phase self-assembly presents a diverse toolbox for engineering new materials with tunable and pre-determined nanostructures that can have various end applications such as in drug delivery, biomineralization and electronics. Self-assembled cages are especially advantageous as the cage geometry provides three distinct functional sites: the interior, the exterior and the solvent-cage interface. In this poster, syntheses and characterization of a peptide cage based on computationally designed homotetrameric coiled coil bundles as building blocks is discussed. Techniques such as Transmission Electron Microscopy (TEM), Small-Angle Neutron Scattering (SANS) and Analytical Ultracentrifugation (AUC) are employed to characterize the size, shape and molecular weight of the self-assembled peptide cages under different pH and temperature conditions. Various self-assembly pathways such as dialysis and thermal quenching are shown to have a significant impact on the final structure of these peptides in solution. Comparison of results with the target cage design can be used to iteratively improve the peptide design and provide greater understanding of its interactions and folding.

High laser efficiency and photostability of pyrromethene dyes mediated by nonpolar solvent.

PubMed

Gupta, Monika; Kamble, Priyadarshini; Rath, M C; Naik, D B; Ray, Alok K

2015-08-10

Many pyrromethene (PM) dyes have been shown to outperform established rhodamine dyes in terms of laser efficiency in the green-yellow spectral region, but their rapid photochemical degradation in commonly used ethanol or methanol solvents continues to limit its use in high average power liquid dye lasers. A comparative study on narrowband laser efficiency and photostability of commercially available PM567 and PM597 dyes, using nonpolar n-heptane and 1,4-dioxane and polar ethanol solvents, was carried out by a constructed pulsed dye laser, pumped by the second harmonic (532 nm) radiation of a Q-switched Nd:YAG laser. Interestingly, both nonpolar solvents showed a significantly higher laser photostability (∼100 times) as well as peak efficiency (∼5%) of these PM dyes in comparison to ethanol. The different photostability of the PM dyes was rationalized by determining their triplet-state spectra and capability to generate reactive singlet oxygen (O₂1) by energy transfer to dissolved oxygen in these solvents using pulse radiolysis. Heptane is identified as a promising solvent for these PM dyes for use in high average power dye lasers, pumped by copper vapor lasers or diode-pumped solid-state green lasers.

Study of polymorphic control in an ethanol-water binary solvent

NASA Astrophysics Data System (ADS)

Kitano, Hiroshi; Tanaka, Takayuki; Hirasawa, Izumi

2017-07-01

Three polymorphs of L-Citrulline crystals, anhydrate (Form α, γ and δ) and pseudo polymorph (dihydrate), were confirmed. In this study, polymorphic control of L-Citrulline was attempted by changing the ethanol concentration in ethanol-water binary solvents. First, each polymorph of L-Citrulline crystals was added to the prepared ethanol-water binary solvents and samples which were obtained chronologically were measured by XRD. Also, the crystal sizes and shapes in transformation were observed by microscope. Then, polymorphs of the crystals after transformation were determined by XRD pattern. As a result, the transformation from dihydrate to anhydrate was observed by adding dihydrate crystals to the ethanol-water binary solvent. Similarly, the transformation from anhydrate to another anhydrate was observed. Especially in the case of adding dihydrate, the existences of all polymorphs were confirmed by adjusting ethanol-water binary solvent. According to the results, it was revealed that polymorphic transformation was affected by the trace amount of water contained in ethanol-water binary solvent. Moreover, transformation from dihydrate to anhydrate was constructed with three phases, dissolution of dihydrate, nucleation and growth of anhydrate. Therefore, the solution-mediated polymorphic transformation was supposed to be a key mechanism for this transformation.

Interfacial free energy governs single polystyrene chain collapse in water and aqueous solutions.

PubMed

Li, Isaac T S; Walker, Gilbert C

2010-05-12

The hydrophobic interaction is significantly responsible for driving protein folding and self-assembly. To understand it, the thermodynamics, the role of water structure, the dewetting process surrounding hydrophobes, and related aspects have undergone extensive investigations. Here, we examine the hypothesis that polymer-solvent interfacial free energy is adequate to describe the energetics of the collapse of a hydrophobic homopolymer chain at fixed temperature, which serves as a much simplified model for studying the hydrophobic collapse of a protein. This implies that changes in polymer-solvent interfacial free energy should be directly proportional to the force to extend a collapsed polymer into a bad solvent. To test this hypothesis, we undertook single-molecule force spectroscopy on a collapsed, single, polystyrene chain in water-ethanol and water-salt mixtures where we measured the monomer solvation free energy from an ensemble average conformations. Different proportions within the binary mixture were used to create solvents with different interfacial free energies with polystyrene. In these mixed solvents, we observed a linear correlation between the interfacial free energy and the force required to extend the chain into solution, which is a direct measure of the solvation free energy per monomer on a single chain at room temperature. A simple analytical model compares favorably with the experimental results. This knowledge supports a common assumption that explicit water solvent may not be necessary for cases whose primary concerns are hydrophobic interactions and hydrophobic hydration.

Tannase-mediated biotransformation assisted separation and purification of theaflavin and epigallocatechin by high speed counter current chromatography and preparative high performance liquid chromatography: A comparative study.

PubMed

Xia, Guobin; Lin, Chunfang; Liu, Songbai

2016-09-01

A large scale isolation and purification of theaflavin (TF) and epigallocatechin (EGC) has been successfully developed by tannase-mediated biotransformation combining high-speed countercurrent chromatography. After tannase hydrolysis of a commercially available theaflavins extract (TE), the content of TF and EGC in tannase-mediated biotransformation product (TBP) achieved approximately 3 times enrichment. SEM studies revealed smooth tannase biotransformation and the possibility of recovery of the tannase. A single 1.5 hours' HSCCC separation for TF and EGC employing a two-phase solvent system could simultaneously produce 180.8 mg of 97.3% purity TF and 87.5 mg of 97.3% purity EGC. However, a preparative HPLC separation of maximum injection volume containing 120 mg TBP prepared 11.2 mg TF of 94.9% purity and 7.7 mg EGC of 89.9% purity. HSCCC separation demonstrated significant advantages over Prep HPLC in terms of sample loading size, separation time, environmental friendly solvent systems, and the production. © 2016 Wiley Periodicals, Inc.

Conceptual, self-assembling graphene nanocontainers

NASA Astrophysics Data System (ADS)

Boothroyd, Simon; Anwar, Jamshed

2015-07-01

We show that graphene nano-sheets, when appropriately functionalised, can form self-assembling nanocontainers which may be opened or closed using a chemical trigger such as pH or polarity of solvent. Conceptual design rules are presented for different container structures, whose ability to form and encapsulate guest molecules is verified by molecular dynamics simulations. The structural simplicity of the graphene nanocontainers offers considerable scope for scaling the capacity, modulating the nature of the internal environment, and defining the trigger for encapsulation or release of the guest molecule(s). This design study will serve to provide additional impetus to developing synthetic approaches for selective functionalisation of graphene.

Eco-friendly microwave-assisted protocol to prepare hyaluronan-fatty acid conjugates and to induce their self-assembly process.

PubMed

Calce, Enrica; Mercurio, Flavia Anna; Leone, Marilisa; Saviano, Michele; De Luca, Stefania

2016-06-05

An environmentally sustainable and energy-efficient synthetic process has been developed to prepare hyaluronan-based nano-sized material. It consists in a microwave-promoted acylation of the hydroxyl function of the polysaccharide with natural fatty acids, performed under solvent-free conditions. The efficient interaction of the solid reagents with the MW radiation accounts for the obtained high yielded products. The self-assembly process of the obtained compounds very fast occurred in an aqueous medium under MW-radiation, thus allowing the development of a green protocol for the nano-particles preparation. Copyright © 2016 Elsevier Ltd. All rights reserved.

Binary Polymer Brushes of Strongly Immiscible Polymers.

PubMed

Chu, Elza; Babar, Tashnia; Bruist, Michael F; Sidorenko, Alexander

2015-06-17

The phenomenon of microphase separation is an example of self-assembly in soft matter and has been observed in block copolymers (BCPs) and similar materials (i.e., supramolecular assemblies (SMAs) and homo/block copolymer blends (HBCs)). In this study, we use microphase separation to construct responsive polymer brushes that collapse to generate periodic surfaces. This is achieved by a chemical reaction between the minor block (10%, poly(4-vinylpyridine)) of the block copolymer and a substrate. The major block of polystyrene (PS) forms mosaic-like arrays of grafted patches that are 10-20 nm in size. Depending on the nature of the assembly (SMA, HBC, or neat BCP) and annealing method (exposure to vapors of different solvents or heating above the glass transition temperature), a range of "mosaic" brushes with different parameters can be obtained. Successive grafting of a secondary polymer (polyacrylamide, PAAm) results in the fabrication of binary polymer brushes (BPBs). Upon being exposed to specific selective solvents, BPBs may adopt different conformations. The surface tension and adhesion of the binary brush are governed by the polymer occupying the top stratum. The "mosaic" brush approach allows for a combination of strongly immiscible polymers in one brush. This facilitates substantial contrast in the surface properties upon switching, previously only possible for substrates composed of predetermined nanostructures. We also demonstrate a possible application of such PS/PAAm brushes in a tunable bioadhesion-bioadhesive (PS on top) or nonbioadhesive (PAAm on top) surface as revealed by Escherichia coli bacterial seeding.

Self-assembly and omniphobic property of fluorinated unit end-functionalized poly(methyl methacrylate)

NASA Astrophysics Data System (ADS)

Junyan, Liang; Pingdi, Xu; Jingxian, Bao; Ling, He; Nan, Zhu

2018-03-01

The self-assembly behavior of fluorinated unit end-functionalized poly(methyl methacrylate) (PDFHM-ef-PMMA) in solution and its influence on the surface microstructure, elemental composition and omniphobic property of cast film was investigated in this work. Specifically, three mixed solutions of tetrahydrofuran (THF)/methanol (MeOH), THF/H2O and THF/H2O/MeOH in various compositions were employed separately as the selective solvents. In THF/MeOH solution, the aggregate morphologies of PDFHM-ef-PMMA changed gradually from core-shell spheres to worm, and then to elliptical vesicles as MeOH content increased. In THF/H2O solution, spherical and bowl-shaped aggregates with significantly larger sizes than those in THF/MeOH solution were favored despite lower H2O content. The further addition of MeOH to THF/H2O mixture could reduce the size of aggregate but hardly change original aggregate morphology. During the film formation process, those self-assembled aggregates in THF/MeOH solution fused with one another to form a smooth surface. When such surface was fully covered by fluorinated segments, the outstanding hexadecane and water slide-off properties and ink-resistant property required for antifouling application were demonstrated. Instead, the aggregates formed in THF/H2O/MeOH mixture were subjected to secondary aggregation of PDFHM-ef-PMMA chains during solvent evaporation, leading to the formation of a particulate film with poor adhesion towards glass plate and hexadecane-repellent property.

Mechanistic insights for block copolymer morphologies: how do worms form vesicles?

PubMed

Blanazs, Adam; Madsen, Jeppe; Battaglia, Giuseppe; Ryan, Anthony J; Armes, Steven P

2011-10-19

Amphiphilic diblock copolymers composed of two covalently linked, chemically distinct chains can be considered to be biological mimics of cell membrane-forming lipid molecules, but with typically more than an order of magnitude increase in molecular weight. These macromolecular amphiphiles are known to form a wide range of nanostructures (spheres, worms, vesicles, etc.) in solvents that are selective for one of the blocks. However, such self-assembly is usually limited to dilute copolymer solutions (<1%), which is a significant disadvantage for potential commercial applications such as drug delivery and coatings. In principle, this problem can be circumvented by polymerization-induced block copolymer self-assembly. Here we detail the synthesis and subsequent in situ self-assembly of amphiphilic AB diblock copolymers in a one pot concentrated aqueous dispersion polymerization formulation. We show that spherical micelles, wormlike micelles, and vesicles can be predictably and efficiently obtained (within 2 h of polymerization, >99% monomer conversion) at relatively high solids in purely aqueous solution. Furthermore, careful monitoring of the in situ polymerization by transmission electron microscopy reveals various novel intermediate structures (including branched worms, partially coalesced worms, nascent bilayers, "octopi", "jellyfish", and finally pure vesicles) that provide important mechanistic insights regarding the evolution of the particle morphology during the sphere-to-worm and worm-to-vesicle transitions. This environmentally benign approach (which involves no toxic solvents, is conducted at relatively high solids, and requires no additional processing) is readily amenable to industrial scale-up, since it is based on commercially available starting materials.

Improved synthesis of phosphatidylserine using bio-based solvents, limonene and p-cymene.

PubMed

Bi, Yan-Hong; Duan, Zhang-Qun; Du, Wen-Ying; Wang, Zhao-Yu

2015-01-01

The bio-based solvents limonene and p-cymene obtained from citrus waste were innovatively employed as the reaction media for enzymatic synthesis of phosphatidylserine. (R)-(+)-Limonene, which is available in large quantities from citrus waste, and its close derivative p-cymene, are promising green solvents. Herein, they were successfully employed as reaction media for enzyme-mediated transphosphatidylation of phosphatidylcholine with L-serine for phosphatidylserine synthesis for the first time. A 95 % yield of phosphatidylserine was achieved after 12 h and the side-reactions (which are the undesirable hydrolysis of phosphatidylcholine and phosphatidylserine) did not happen. This work presents an alternative strategy for preparing phosphatidylserine that possesses obvious advantages over the traditional processes in terms of high efficiency combined with environmental friendliness.

Dispersal and neutral sampling mediate contingent effects of disturbance on plant beta-diversity: a meta-analysis.

PubMed

Catano, Christopher P; Dickson, Timothy L; Myers, Jonathan A

2017-03-01

A major challenge in ecology, conservation and global-change biology is to understand why biodiversity responds differently to similar environmental changes. Contingent biodiversity responses may depend on how disturbance and dispersal interact to alter variation in community composition (β-diversity) and assembly mechanisms. However, quantitative syntheses of these patterns and processes across studies are lacking. Using null-models and meta-analyses of 22 factorial experiments in herbaceous plant communities across Europe and North America, we show that disturbance diversifies communities when dispersal is limited, but homogenises communities when combined with increased immigration from the species pool. In contrast to the hypothesis that disturbance and dispersal mediate the strength of niche assembly, both processes altered β-diversity through neutral-sampling effects on numbers of individuals and species in communities. Our synthesis suggests that stochastic effects of disturbance and dispersal on community assembly play an important, but underappreciated, role in mediating biotic homogenisation and biodiversity responses to environmental change. © 2017 John Wiley & Sons Ltd/CNRS.

Selective self-assembly of adenine-silver nanoparticles forms rings resembling the size of cells

PubMed Central

Choi, Sungmoon; Park, Soonyoung; Yang, Seon-Ah; Jeong, Yujin; Yu, Junhua

2015-01-01

Self-assembly has played critical roles in the construction of functional nanomaterials. However, the structure of the macroscale multicomponent materials built by the self-assembly of nanoscale building blocks is hard to predict due to multiple intermolecular interactions of great complexity. Evaporation of solvents is usually an important approach to induce kinetically stable assemblies of building blocks with a large-scale specific arrangement. During such a deweting process, we tried to monitor the possible interactions between silver nanoparticles and nucleobases at a larger scale by epifluorescence microscopy, thanks to the doping of silver nanoparticles with luminescent silver nanodots. ssDNA oligomer-stabilized silver nanoparticles and adenine self-assemble to form ring-like compartments similar to the size of modern cells. However, the silver ions only dismantle the self-assembly of adenine. The rings are thermodynamically stable as the drying process only enrich the nanoparticles-nucleobase mixture to a concentration that activates the self-assembly. The permeable membrane-like edge of the ring is composed of adenine filaments glued together by silver nanoparticles. Interestingly, chemicals are partially confined and accumulated inside the ring, suggesting that this might be used as a microreactor to speed up chemical reactions during a dewetting process. PMID:26643504

Impact of Linear Alkyl Length on the Assembly of Twisted Perylene Bisimides: From Molecular Arrangement to Nanostructures.

PubMed

Guo, Zongxia; Wang, Kun; Yu, Ping; Wang, Xiangnan; Lan, Shusha; Sun, Kai; Yi, Yuanping; Li, Zhibo

2017-11-02

The effect of the length of linear alkyl chains substituted at imine positions on the assembly of tetrachlorinated perylene bisimides (1: PBI with -C 6 H 13 ; 2: PBI with -C 12 H 25 ) has been investigated. Solvent-induced assembly was performed in solutions of THF and methanol with varying volume ratios. Morphological (SEM, AFM, and TEM) and spectral (UV/Vis, fluorescence, FTIR, and XRD) methods were used to characterize the assembled nanostructures and the molecular arrangement in the aggregates. It was found that uniform structures could be obtained for both molecules in solutions with a high ratio of methanol. PBI 1 formed rigid nanosheets, whereas 2 assembled into longer nanostripes with a high ratio of length to width. On combining the morphological data with the spectral data, it was suggested that π-π stacking predominated in assemblies of 1, and the synergetic effect of van der Waals interactions from the long alkyl chains and π-π stacking between neighboring building blocks facilitated the growth of the long-range-ordered nanostructures of 2. By changing the linear chain length, the hierarchical assembly of PBIs modified on bay positions could be manipulated effectively. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Micellar Self-Assembly of Recombinant Resilin-/Elastin-Like Block Copolypeptides.

PubMed

Weitzhandler, Isaac; Dzuricky, Michael; Hoffmann, Ingo; Garcia Quiroz, Felipe; Gradzielski, Michael; Chilkoti, Ashutosh

2017-08-14

Reported here is the synthesis of perfectly sequence defined, monodisperse diblock copolypeptides of hydrophilic elastin-like and hydrophobic resilin-like polypeptide blocks and characterization of their self-assembly as a function of structural parameters by light scattering, cryo-TEM, and small-angle neutron scattering. A subset of these diblock copolypeptides exhibit lower critical solution temperature and upper critical solution temperature phase behavior and self-assemble into spherical or cylindrical micelles. Their morphologies are dictated by their chain length, degree of hydrophilicity, and hydrophilic weight fraction of the ELP block. We find that (1) independent of the length of the corona-forming ELP block there is a minimum threshold in the length of the RLP block below which self-assembly does not occur, but that once that threshold is crossed, (2) the RLP block length is a unique molecular parameter to independently tune self-assembly and (3) increasing the hydrophobicity of the corona-forming ELP drives a transition from spherical to cylindrical morphology. Unlike the self-assembly of purely ELP-based block copolymers, the self-assembly of RLP-ELPs can be understood by simple principles of polymer physics relating hydrophilic weight fraction and polymer-polymer and polymer-solvent interactions to micellar morphology, which is important as it provides a route for the de novo design of desired nanoscale morphologies from first principles.

Intramolecular, Exciplex-Mediated, Proton-Coupled, Charge-Transfer Processes in N,N-Dimethyl-3-(1-pyrenyl)propan-1-ammonium Cations: Influence of Anion, Solvent Polarity, and Temperature.

PubMed

Safko, Trevor M; Faleiros, Marcelo M; Atvars, Teresa D Z; Weiss, Richard G

2016-06-16

An intramolecular exciplex-mediated, proton-coupled, charge-transfer (PCCT) process has been investigated for a series of N,N-dimethyl-3-(1-pyrenyl)propan-1-ammonium cations with different anions (PyS) in solvents of low to intermediate polarity over a wide temperature range. Solvent mediates both the equilibrium between conformations of the cation that place the pyrenyl and ammonium groups in proximity (conformation C) or far from each other (conformation O) and the ability of the ammonium group to transfer a proton adiabatically in the PyS excited singlet state. Thus, exciplex emission, concurrent with the PCCT process, was observed only in hydrogen-bond accepting solvents of relatively low polarity (tetrahydrofuran, ethyl acetate, and 1,4-dioxane) and not in dichloromethane. From the exciplex emission and other spectroscopic and thermodynamic data, the acidity of the ammonium group in conformation C of the excited singlet state of PyS (pKa*) has been estimated to be ca. -3.4 in tetrahydrofuran. The ratios between the intensities of emission from the exciplex and the locally excited state (IEx/ILE) appear to be much more dependent on the nature of the anion than are the rates of exciplex formation and decay, although the excited state data do not provide a quantitative measure of the anion effect on the C-O equilibrium. The activation energies associated with exciplex formation in THF are calculated to be 0.08 to 0.15 eV lower than for the neutral amine, N,N-dimethyl-3-(1-pyrenyl)propan-1-amine. Decay of the exciplexes formed from the deprotonation of PyS is hypothesized to occur through charge-recombination processes. To our knowledge, this is the first example in which photoacidity and intramolecular exciplex formation (i.e., a PCCT reaction) are coupled.

Anti-cooperative supramolecular polymerization: a new K2-K model applied to the self-assembly of perylene bisimide dye proceeding via well-defined hydrogen-bonded dimers.

PubMed

Gershberg, Jana; Fennel, Franziska; Rehm, Thomas H; Lochbrunner, Stefan; Würthner, Frank

2016-03-01

A perylene bisimide dye bearing amide functionalities at the imide positions derived from amino acid l-alanine and a dialkoxy-substituted benzyl amine self-assembles into tightly bound dimers by π-π-stacking and hydrogen bonding in chloroform. In less polar or unpolar solvents like toluene and methylcyclohexane, and in their mixtures, these dimers further self-assemble into extended oligomeric aggregates in an anti-cooperative process in which even numbered aggregates are highly favoured. The stepwise transition from dimers into oligomers can not be properly described by conventional K 2 - K model, and thus a new K 2 - K aggregation model has been developed, which interpretes the present anti-cooperative supramolecular polymerization more appropriately. The newly developed K 2 - K model will be useful to describe self-assembly processes of a plethora of other π-conjugated molecules that are characterized by a favored dimer species.

Self-Assembly of Diblock Molecular Polymer Brushes in the Spherical Confinement of Nanoemulsion Droplets.

PubMed

Steinhaus, Andrea; Pelras, Théophile; Chakroun, Ramzi; Gröschel, André H; Müllner, Markus

2018-05-02

Understanding the self-assembly behavior of polymers of various topologies is key to a reliable design of functional polymer materials. Self-assembly under confinement conditions emerges as a versatile avenue to design polymer particles with complex internal morphologies while simultaneously facilitating scale-up. However, only linear block copolymers have been studied to date, despite the increasing control over macromolecule composition and architecture available. This study extends the investigation of polymer self-assembly in confinement from regular diblock copolymers to diblock molecular polymer brushes (MPBs). Block-type MPBs with polystyrene (PS) and polylactide (PLA) compartments of different sizes are incorporated into surfactant-stabilized oil-in-water (chloroform/water) emulsions. The increasing confinement in the nanoemulsion droplets during solvent evaporation directs the MPBs to form solid nano/microparticles. Microscopy studies reveal an intricate internal particle structure, including interpenetrating networks and axially stacked lamellae of PS and PLA, depending on the PS/PLA ratio of the brushes. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis, optical properties, and helical self-assembly of a bivaline-containing tetraphenylethene

NASA Astrophysics Data System (ADS)

Li, Hongkun; Zheng, Xiaoyan; Su, Huimin; Lam, Jacky W. Y.; Sing Wong, Kam; Xue, Shan; Huang, Xuejiao; Huang, Xuhui; Li, Bing Shi; Tang, Ben Zhong

2016-01-01

A chiral tetraphenylethene derivative with two valine-containing attachments (TPE-DVAL), was synthesized by Cu(I)-catalyzed azide-alkyne “click” reaction. The optical properties and self-assembling behaviours of TPE-DVAL were investigated. The molecule is non-emissive and circular dichroism (CD)-silent in solution, but shows strong fluorescence and Cotton effects in the aggregation state, demonstrating aggregation-induced emission (AIE) and CD (AICD) characteristics. TPE-DVAL exhibits good circularly polarized luminescence (CPL) when depositing on the surface of quartz to allow the evaporation of its 1,2-dichloroethane solution. SEM and TEM images of the molecule show that the molecule readily self-assembles into right-handed helical nanofibers upon the evaporation of its solvent of DCE. The molecular alignments and interactions in assembling process are further explored through XRD analysis and computational simulation. The driving forces for the formation of the helical fibers were from the cooperative effects of intermolecular hydrogen bonding, π-π interactions and steric effect.

Octanol-assisted liposome assembly on chip

PubMed Central

Deshpande, Siddharth; Caspi, Yaron; Meijering, Anna E. C.; Dekker, Cees

2016-01-01

Liposomes are versatile supramolecular assemblies widely used in basic and applied sciences. Here we present a novel microfluidics-based method, octanol-assisted liposome assembly (OLA), to form monodisperse, cell-sized (5–20 μm), unilamellar liposomes with excellent encapsulation efficiency. Akin to bubble blowing, an inner aqueous phase and a surrounding lipid-carrying 1-octanol phase is pinched off by outer fluid streams. Such hydrodynamic flow focusing results in double-emulsion droplets that spontaneously develop a side-connected 1-octanol pocket. Owing to interfacial energy minimization, the pocket splits off to yield fully assembled solvent-free liposomes within minutes. This solves the long-standing fundamental problem of prolonged presence of residual oil in the liposome bilayer. We demonstrate the unilamellarity of liposomes with functional α-haemolysin protein pores in the membrane and validate the biocompatibility by inner leaflet localization of bacterial divisome proteins (FtsZ and ZipA). OLA offers a versatile platform for future analytical tools, delivery systems, nanoreactors and synthetic cells. PMID:26794442

Octanol-assisted liposome assembly on chip.

PubMed

Deshpande, Siddharth; Caspi, Yaron; Meijering, Anna E C; Dekker, Cees

2016-01-22

Liposomes are versatile supramolecular assemblies widely used in basic and applied sciences. Here we present a novel microfluidics-based method, octanol-assisted liposome assembly (OLA), to form monodisperse, cell-sized (5-20 μm), unilamellar liposomes with excellent encapsulation efficiency. Akin to bubble blowing, an inner aqueous phase and a surrounding lipid-carrying 1-octanol phase is pinched off by outer fluid streams. Such hydrodynamic flow focusing results in double-emulsion droplets that spontaneously develop a side-connected 1-octanol pocket. Owing to interfacial energy minimization, the pocket splits off to yield fully assembled solvent-free liposomes within minutes. This solves the long-standing fundamental problem of prolonged presence of residual oil in the liposome bilayer. We demonstrate the unilamellarity of liposomes with functional α-haemolysin protein pores in the membrane and validate the biocompatibility by inner leaflet localization of bacterial divisome proteins (FtsZ and ZipA). OLA offers a versatile platform for future analytical tools, delivery systems, nanoreactors and synthetic cells.

Octanol-assisted liposome assembly on chip

NASA Astrophysics Data System (ADS)

Deshpande, Siddharth; Caspi, Yaron; Meijering, Anna E. C.; Dekker, Cees

2016-01-01

Liposomes are versatile supramolecular assemblies widely used in basic and applied sciences. Here we present a novel microfluidics-based method, octanol-assisted liposome assembly (OLA), to form monodisperse, cell-sized (5-20 μm), unilamellar liposomes with excellent encapsulation efficiency. Akin to bubble blowing, an inner aqueous phase and a surrounding lipid-carrying 1-octanol phase is pinched off by outer fluid streams. Such hydrodynamic flow focusing results in double-emulsion droplets that spontaneously develop a side-connected 1-octanol pocket. Owing to interfacial energy minimization, the pocket splits off to yield fully assembled solvent-free liposomes within minutes. This solves the long-standing fundamental problem of prolonged presence of residual oil in the liposome bilayer. We demonstrate the unilamellarity of liposomes with functional α-haemolysin protein pores in the membrane and validate the biocompatibility by inner leaflet localization of bacterial divisome proteins (FtsZ and ZipA). OLA offers a versatile platform for future analytical tools, delivery systems, nanoreactors and synthetic cells.

Evaluation of Isoprene Chain Extension from PEO Macromolecular Chain Transfer Agents for the Preparation of Dual, Invertible Block Copolymer Nanoassemblies.

PubMed

Bartels, Jeremy W; Cauët, Solène I; Billings, Peter L; Lin, Lily Yun; Zhu, Jiahua; Fidge, Christopher; Pochan, Darrin J; Wooley, Karen L

2010-09-14

Two RAFT-capable PEO macro-CTAs, 2 and 5 kDa, were prepared and used for the polymerization of isoprene which yielded well-defined block copolymers of varied lengths and compositions. GPC analysis of the PEO macro-CTAs and block copolymers showed remaining unreacted PEO macro-CTA. Mathematical deconvolution of the GPC chromatograms allowed for the estimation of the blocking efficiency, about 50% for the 5 kDa PEO macro-CTA and 64% for the 2 kDa CTA. Self assembly of the block copolymers in both water and decane was investigated and the resulting regular and inverse assemblies, respectively, were analyzed with DLS, AFM, and TEM to ascertain their dimensions and properties. Assembly of PEO-b-PIp block copolymers in aqueous solution resulted in well-defined micelles of varying sizes while the assembly in hydrophobic, organic solvent resulted in the formation of different morphologies including large aggregates and well-defined cylindrical and spherical structures.

Surface Pb nanoparticle aggregation, coalescence and differential capacitance in a deep eutectic solvent using a simultaneous sample-rotated small angle x-ray scattering and electrochemical methods approach [Surface Pb nanoparticle aggregation, coalescence and differential capacitance in a deep eutectic solvent using a simultaneous grazing transmission small angle x-ray scattering and electrochemical methods approach

DOE PAGES

Hammons, Joshua A.; Ilavsky, Jan

2017-01-18

Nanoparticle electrodeposition is a simple and scalable approach to synthesizing supported nanoparticles. Used with a deep eutectic solvent (DES), surface nanoparticles can be assembled and exhibit unique surface charge separation when the DES is adsorbed on the nanoparticle surface. Key to understanding and controlling the assembly and the capacitance is a thorough understanding of surface particle mobility and charge screening, which requires an in-situ approach. In this study, Pb particle formation, size, shape and capacitance are resolved in a 1:2 choline Cl –: urea deep eutectic solvent whilst sweeping the cell potential in the range: 0.2 V to –1.2 Vmore » (vs. Ag/AgCl). These system parameters were resolved using a complementary suite of sample-rotated small angle X-ray scattering (SR-SAXS) and electrochemical impedance spectroscopy (EIS), which are presented and discussed in detail. This approach is able to show that both particle and ion transport are impeded in the DES, as aggregation occurs over the course of 6 minutes, and dissolved Pb ions accumulate and remain near the surface after a nucleation pulse is applied. The DES-Pb interactions strongly depend on the cell potential as evidenced by the specific differential capacitance of the Pb deposit, which has a maximum value of 2.5 +/– 0.5 F g –1 at –1.0 V vs. Ag/AgCl. Together, the SR-SAXS-EIS approach is able to characterize the unique nanoparticle capacitance, mobility and ion mobility in a DES and can be used to study a wide range of nanoparticle deposition systems in-situ.« less

Surface Pb nanoparticle aggregation, coalescence and differential capacitance in a deep eutectic solvent using a simultaneous sample-rotated small angle x-ray scattering and electrochemical methods approach [Surface Pb nanoparticle aggregation, coalescence and differential capacitance in a deep eutectic solvent using a simultaneous grazing transmission small angle x-ray scattering and electrochemical methods approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hammons, Joshua A.; Ilavsky, Jan

Nanoparticle electrodeposition is a simple and scalable approach to synthesizing supported nanoparticles. Used with a deep eutectic solvent (DES), surface nanoparticles can be assembled and exhibit unique surface charge separation when the DES is adsorbed on the nanoparticle surface. Key to understanding and controlling the assembly and the capacitance is a thorough understanding of surface particle mobility and charge screening, which requires an in-situ approach. In this study, Pb particle formation, size, shape and capacitance are resolved in a 1:2 choline Cl –: urea deep eutectic solvent whilst sweeping the cell potential in the range: 0.2 V to –1.2 Vmore » (vs. Ag/AgCl). These system parameters were resolved using a complementary suite of sample-rotated small angle X-ray scattering (SR-SAXS) and electrochemical impedance spectroscopy (EIS), which are presented and discussed in detail. This approach is able to show that both particle and ion transport are impeded in the DES, as aggregation occurs over the course of 6 minutes, and dissolved Pb ions accumulate and remain near the surface after a nucleation pulse is applied. The DES-Pb interactions strongly depend on the cell potential as evidenced by the specific differential capacitance of the Pb deposit, which has a maximum value of 2.5 +/– 0.5 F g –1 at –1.0 V vs. Ag/AgCl. Together, the SR-SAXS-EIS approach is able to characterize the unique nanoparticle capacitance, mobility and ion mobility in a DES and can be used to study a wide range of nanoparticle deposition systems in-situ.« less

Dimethyl Sulfoxide Protects Escherichia coli from Rapid Antimicrobial-Mediated Killing.

PubMed

Mi, Hongfei; Wang, Dai; Xue, Yunxin; Zhang, Zhi; Niu, Jianjun; Hong, Yuzhi; Drlica, Karl; Zhao, Xilin

2016-08-01

The contribution of reactive oxygen species (ROS) to antimicrobial lethality was examined by treating Escherichia coli with dimethyl sulfoxide (DMSO), an antioxidant solvent frequently used in antimicrobial studies. DMSO inhibited killing by ampicillin, kanamycin, and two quinolones and had little effect on MICs. DMSO-mediated protection correlated with decreased ROS accumulation and provided evidence for ROS-mediated programmed cell death. These data support the contribution of ROS to antimicrobial lethality and suggest caution when using DMSO-dissolved antimicrobials for short-time killing assays. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

Physicochemical and catalytic properties of Au nanorods micro-assembled in solvents of varying dipole moment and refractive index

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaur, Rupinder; Pal, Bonamali, E-mail: bpal@thapar.edu

2015-02-15

Highlights: • Physicochemical activities of Au nanorods in water largely differ from organic solvents. • Au nanorods agglomeration increased with dipole moments of different polar solvents. • Refractive indexes of Au nanorods dispersion in various polar solvents are enhanced. • Electrokinetics significantly altered depending on agglomerated size of Au nanorods. • Catalysis or co-catalysis activity is varied as per the extent of Au nanorods coagulation. - Abstract: This paper deals with the impact of dipole moment (1.66–3.96 D) and refractive index (1.333–1.422) of the dispersion solvent on the plasmon absorption, surface charge, zeta potential, and adsorption properties of Au nanorodsmore » (AuNRs). AuNRs (length ≈ 53 nm and width ≈ 20 nm) undergo agglomeration (size 50–180 nm) with increase in the dipole moment of solvent (iPrOH < MeOH < DMF < DMSO). Whereas, no such coagulation occurs in H{sub 2}O and CCl{sub 4} suspension as confirmed by DLS and TEM size distribution. The electrostatic interaction of AuNRs with its surface adsorbed solvent dipoles leads to alteration of the their ionic state, absolute electronic charge and zeta potential (+49.79 mV in H{sub 2}O, +8.99 mV in DMF and −4.65 mV in MeOH dispersion) to a greater extent. This interaction distinctly modifies the adsorption behavior of polar molecules like p-nitrophenol and salicylic acid on AuNRs surface, as evidenced by the measured changes in their electro-kinetic parameters. As a result, we observe a substantial difference in catalytic and co-catalytic activities of AuNRs dispersed in various solvents as mentioned above because the catalytic properties of AuNRs are strongly dependent on the type of solvent in which they are dispersed.« less

Highly selective and sensitive method for Cu2 + detection based on chiroptical activity of L-Cysteine mediated Au nanorod assemblies

NASA Astrophysics Data System (ADS)

Abbasi, Shahryar; Khani, Hamzeh

2017-11-01

Herein, we demonstrated a simple and efficient method to detect Cu2 + based on amplified optical activity in the chiral nanoassemblies of gold nanorods (Au NRs). L-Cysteine can induce side-by-side or end-to-end assembly of Au NRs with an evident plasmonic circular dichroism (PCD) response due to coupling between surface plasmon resonances (SPR) of Au NRs and the chiral signal of L-Cys. Because of the obvious stronger plasmonic circular dichrosim (CD) response of the side-by-side assembly compared with the end-to-end assemblies, SS assembled Au NRs was selected as a sensitive platform and used for Cu2 + detection. In the presence of Cu2 +, Cu2 + can catalyze O2 oxidation of cysteine to cystine. With an increase in Cu2 + concentration, the L-Cysteine-mediated assembly of Au NRs decreased because of decrease in the free cysteine thiol groups, and the PCD signal decreased. Taking advantage of this method, Cu2 + could be detected in the concentration range of 20 pM-5 nM. Under optimal conditions, the calculated detection limit was found to be 7 pM.

Assembly of high density lipoprotein by the ABCA1/apolipoprotein pathway.

PubMed

Yokoyama, Shinji

2005-06-01

Mammalian somatic cells do not catabolize cholesterol and therefore need to export it for sterol homeostasis at the levels of cells and whole bodies. This mechanism may reduce intracellularly accumulated cholesterol in excess, and thereby would contribute to the prevention or cure of the initial stage of atherosclerotic vascular lesions. HDL is thought to play a main role in this reaction on the basis of epidemiological evidence and in-vitro experimental data. Two independent mechanisms have been identified for this reaction. One is non-specific diffusion-mediated cholesterol 'efflux' from the cell surface, and cholesterol is trapped by various extracellular acceptors including lipoproteins. Extracellular cholesterol esterification on HDL provides a driving force for the net removal of cell cholesterol, and some cellular factors may enhance this reaction. The other mechanism is an apolipoprotein-mediated process to generate HDL by removing cellular phospholipid and cholesterol. This reaction is mediated by a membrane protein ABCA1, and lipid-free or lipid-poor helical apolipoproteins recruit cellular phospholipid and cholesterol to assemble HDL particles. The reaction is composed of two elements: the assembly of HDL particles with phospholipid by apolipoprotein, and cholesterol enrichment in HDL. ABCA1 is essential for the former step, and the latter step requires further intracellular events. ABCA1 is a rate-limiting factor of HDL assembly and is regulated by transcriptional factors and posttranscriptional factors. Posttranscriptional regulation of ABCA1 involves the modulation of its calpain-mediated degradation.

Trait-mediated assembly processes predict successional changes in community diversity of tropical forests.

PubMed

Lasky, Jesse R; Uriarte, María; Boukili, Vanessa K; Chazdon, Robin L

2014-04-15

Interspecific differences in relative fitness can cause local dominance by a single species. However, stabilizing interspecific niche differences can promote local diversity. Understanding these mechanisms requires that we simultaneously quantify their effects on demography and link these effects to community dynamics. Successional forests are ideal systems for testing assembly theory because they exhibit rapid community assembly. Here, we leverage functional trait and long-term demographic data to build spatially explicit models of successional community dynamics of lowland rainforests in Costa Rica. First, we ask what the effects and relative importance of four trait-mediated community assembly processes are on tree survival, a major component of fitness. We model trait correlations with relative fitness differences that are both density-independent and -dependent in addition to trait correlations with stabilizing niche differences. Second, we ask how the relative importance of these trait-mediated processes relates to successional changes in functional diversity. Tree dynamics were more strongly influenced by trait-related interspecific variation in average survival than trait-related responses to neighbors, with wood specific gravity (WSG) positively correlated with greater survival. Our findings also suggest that competition was mediated by stabilizing niche differences associated with specific leaf area (SLA) and leaf dry matter content (LDMC). These drivers of individual-level survival were reflected in successional shifts to higher SLA and LDMC diversity but lower WSG diversity. Our study makes significant advances to identifying the links between individual tree performance, species functional traits, and mechanisms of tropical forest succession.

Effect of solvents on the enzyme mediated degradation of copolymers

NASA Astrophysics Data System (ADS)

Banerjee, Aditi; Chatterjee, Kaushik; Madras, Giridhar

2015-09-01

The biodegradation of polycaprolactone (PCL), polylactic acid (PLA), polyglycolide (PGA) and their copolymers, poly (lactide-co-glycolide) and poly (D, L-lactide-co-caprolactone) (PLCL) was investigated. The influence of different solvents on the degradation of these polymers at 37 °C in the presence of two different lipases namely Novozym 435 and the free lipase of porcine pancreas was investigated. The rate coefficients for the polymer degradation and enzyme deactivation were determined using continuous distribution kinetics. Among the homopolymers, the degradation of PGA was nearly an order of magnitude lower than that for PCL and PLA. The overall rate coefficients of the copolymers were higher than their respective homopolymers. Thus, PLCL degraded faster than either PCL or PLA. The degradation was highly dependent on the viscosity of the solvent used with the highest degradation observed in acetone. The degradation of the polymers in acetone was nearly twice that observed in dimethyl sulfoxide indicating that the degradation decreases with increase in the solvent viscosity. The degradation of the polymers in water-solvent mixtures indicated an optimal water content of 2.5 wt% of water.

Theory of nematic order with aggregate dehydration for reversibly assembling proteins in concentrated solutions: Application to sickle-cell hemoglobin polymers

NASA Astrophysics Data System (ADS)

Hentschke, Reinhard; Herzfeld, Judith

1991-06-01

The reversible association of globular protein molecules in concentrated solution leads to highly polydisperse fibers, e.g., actin filaments, microtubules, and sickle-cell hemoglobin fibers. At high concentrations, excluded-volume interactions between the fibers lead to spontaneous alignment analogous to that in simple lyotropic liquid crystals. However, the phase behavior of reversibly associating proteins is complicated by the threefold coupling between the growth, alignment, and hydration of the fibers. In protein systems aggregates contain substantial solvent, which may cause them to swell or shrink, depending on osmotic stress. Extending previous work, we present a model for the equilibrium phase behavior of the above-noted protein systems in terms of simple intra- and interaggregate interactions, combined with equilibration of fiber-incorporated solvent with the bulk solvent. Specifically, we compare our model results to recent osmotic pressure data for sickle-cell hemoglobin and find excellent agreement. This comparison shows that particle interactions sufficient to cause alignment are also sufficient to squeeze significant amounts of solvent out of protein fibers. In addition, the model is in accord with findings from independent sedimentation and birefringence studies on sickle-cell hemoglobin.

A track process for solvent annealing of high-χ BCPs

NASA Astrophysics Data System (ADS)

Guerrero, Douglas J.; Sakavuyi, Kaumba; Xu, Kui; Gharbi, Ahmed; Tiron, Raluca; Servin, Isabelle; Pain, Laurent; Claveau, Guillaume; Stokes, Harold; Harumoto, Masahiko; Nicolet, Célia; Chevalier, Xavier

2017-03-01

High chi organic lamellar-forming block copolymers were prepared with 18 nm intrinsic period Lo value. The BCPs were coated on a neutral layer on silicon substrates and were either thermally annealed or exposed to solvent vapors both in a 300mm track. The effect of lowering the glass transition temperature (Tg) on the high chi BCP was investigated. Process temperatures and times were varied. It was found that the BCP having lower Tg exhibits faster kinetics and is able to reach alignment in a shorter time than a similar BCP having higher Tg. Fingerprint defect analysis also shows that the BCP with lower Tg has lower defects. The results show that fingerprint formation can be achieved with either ether or ester type solvents depending on the BCP used. The results show that a track process for solvent annealing of high-χ BCPs is feasible and could provide the path forward for incorporation of BCP in future nodes. Finally, directed self-assembly was demonstrated by implemented high chi polymers on a graphoepitaxy test vehicles. CD and line width roughness was evaluated on patterns with a multiplication factor up to 7.

Association of a multifunctional ionic block copolymer in a selective solvent

DOE PAGES

Etampawala, Thusitha N.; Aryal, Dipak; Osti, Naresh C.; ...

2016-11-14

The self-assembly of multiblock copolymers in solutions is controlled by a delicate balance between inherent phase segregation due to incompatibility of the blocks and the interaction of the individual blocks with the solvent. The current study elucidates the association of pentablock copolymers in a mixture of selective solvents which are good for the hydrophobic segments and poor for the hydrophilic blocks using small angle neutron scattering (SANS). The pentablock consists of a center block of randomly sulfonated polystyrene, designed for transport, tethered to poly-ethylene-r-propylene and end-capped by poly-t-butyl styrene, for mechanical stability. We find that the pentablock forms ellipsoidal core-shellmore » micelles with the sulfonated polystyrene in the core and Gaussian decaying chains of swollen poly-ethylene-r-propylene and poly-t-butyl styrene tertiary in the corona. With increasing solution concentration, the size of the micelle, the thickness of the corona, and the aggregation number increase, while the solvent fraction in the core decreases. As a result, in dilute solution the micelle increases in size as the temperature is increased, however, temperature effects dissipate with increasing solution concentration.« less

Solvent-regulated assemblies of four Zn(II) coordination polymers constructed by flexible tetracarboxylates and pyridyl ligands

NASA Astrophysics Data System (ADS)

Fang, Kang; He, Xiang; Shao, Min; Li, Ming-Xing

2016-08-01

Four unique complexes with diverse coordination architectures were synthesized upon complexation of 5,5-(1,4-phenylenebis (methylene))bis (oxy)- diisophthalic acid (H4L) with zinc ions by using different solvent. namely, {[Zn(H2L) (bpp)]·DEF}n (1), {[Zn2(L) (bpp)2]·4H2O}n (2), {[Zn2(L) (pdp)2]·3H2O·DEF}n (3), {[Zn2(L) (pdp)2].4H2O}n (4). Complexes 1,2 and 3,4 are obtained by varying solvents to control their structures. The size of solvent molecular plays an important role to control different structure of these compounds. Compound 1 is 2D waved framework with (4, 4) grid layer as sql topology. Compound 3 displays a (4,6)-connected 2-nodal net with a fsc topology. Compounds 2 and 4 are all three-dimensional network simplified as (4,4)-connected 2-nodal net with a bbf topology. The photochemical properties of compounds 1-4 were tested in the solid state at room temperature, owing to their strong luminescent emissions, complexes 1-4 are good candidates for photoactive materials.

Mediator binds to boundaries of chromosomal interaction domains and to proteins involved in DNA looping, RNA metabolism, chromatin remodeling, and actin assembly.

PubMed

Chereji, Razvan V; Bharatula, Vasudha; Elfving, Nils; Blomberg, Jeanette; Larsson, Miriam; Morozov, Alexandre V; Broach, James R; Björklund, Stefan

2017-09-06

Mediator is a multi-unit molecular complex that plays a key role in transferring signals from transcriptional regulators to RNA polymerase II in eukaryotes. We have combined biochemical purification of the Saccharomyces cerevisiae Mediator from chromatin with chromatin immunoprecipitation in order to reveal Mediator occupancy on DNA genome-wide, and to identify proteins interacting specifically with Mediator on the chromatin template. Tandem mass spectrometry of proteins in immunoprecipitates of mediator complexes revealed specific interactions between Mediator and the RSC, Arp2/Arp3, CPF, CF 1A and Lsm complexes in chromatin. These factors are primarily involved in chromatin remodeling, actin assembly, mRNA 3'-end processing, gene looping and mRNA decay, but they have also been shown to enter the nucleus and participate in Pol II transcription. Moreover, we have found that Mediator, in addition to binding Pol II promoters, occupies chromosomal interacting domain (CID) boundaries and that Mediator in chromatin associates with proteins that have been shown to interact with CID boundaries, such as Sth1, Ssu72 and histone H4. This suggests that Mediator plays a significant role in higher-order genome organization. © The Author(s) 2017. Published by Oxford University Press on behalf of Nucleic Acids Research.

Controlling wetting and self-assembly dynamics by tailored hydrophobic and oleophobic surfaces.

PubMed

Miele, Ermanno; Malerba, Mario; Dipalo, Michele; Rondanina, Eliana; Toma, Andrea; De Angelis, Francesco

2014-06-25

Tailored hydrophobic and oleophobic surfaces are exploited for controlling the wetting behaviour and evaporation process of solution dropped on them. This enables molecules and nano-objects that are dissolved in water or organic solvents to be delivered and arranged in a well-defined 2D layout. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Self-assembly of palladium nanoparticles: Synthesis of nanobelts, nanoplates and nanotrees using vitamin B1 and their application in carbon-carbon coupling reactions

EPA Science Inventory

An environmentally friendly one-step method to synthesize palladium (Pd) nanobelts, nanoplates and nanotrees using vitamin B1 without using any special capping agents at room temperature is described. This greener method, which uses water as benign solvent and vitamin B1 as a red...

Self-assembled micro-organogels for 3D printing silicone structures.

PubMed

O'Bryan, Christopher S; Bhattacharjee, Tapomoy; Hart, Samuel; Kabb, Christopher P; Schulze, Kyle D; Chilakala, Indrasena; Sumerlin, Brent S; Sawyer, W Gregory; Angelini, Thomas E

2017-05-01

The widespread prevalence of commercial products made from microgels illustrates the immense practical value of harnessing the jamming transition; there are countless ways to use soft, solid materials that fluidize and become solid again with small variations in applied stress. The traditional routes of microgel synthesis produce materials that predominantly swell in aqueous solvents or, less often, in aggressive organic solvents, constraining ways that these exceptionally useful materials can be used. For example, aqueous microgels have been used as the foundation of three-dimensional (3D) bioprinting applications, yet the incompatibility of available microgels with nonpolar liquids, such as oils, limits their use in 3D printing with oil-based materials, such as silicone. We present a method to make micro-organogels swollen in mineral oil, using block copolymer self-assembly. The rheological properties of this micro-organogel material can be tuned, leveraging the jamming transition to facilitate its use in 3D printing of silicone structures. We find that the minimum printed feature size can be controlled by the yield stress of the micro-organogel medium, enabling the fabrication of numerous complex silicone structures, including branched perfusable networks and functional fluid pumps.

"Martinizing" the Variational Implicit Solvent Method (VISM): Solvation Free Energy for Coarse-Grained Proteins.

PubMed

Ricci, Clarisse G; Li, Bo; Cheng, Li-Tien; Dzubiella, Joachim; McCammon, J Andrew

2017-07-13

Solvation is a fundamental driving force in many biological processes including biomolecular recognition and self-assembly, not to mention protein folding, dynamics, and function. The variational implicit solvent method (VISM) is a theoretical tool currently developed and optimized to estimate solvation free energies for systems of very complex topology, such as biomolecules. VISM's theoretical framework makes it unique because it couples hydrophobic, van der Waals, and electrostatic interactions as a functional of the solvation interface. By minimizing this functional, VISM produces the solvation interface as an output of the theory. In this work, we push VISM to larger scale applications by combining it with coarse-grained solute Hamiltonians adapted from the MARTINI framework, a well-established mesoscale force field for modeling large-scale biomolecule assemblies. We show how MARTINI-VISM ( M VISM) compares with atomistic VISM ( A VISM) for a small set of proteins differing in size, shape, and charge distribution. We also demonstrate M VISM's suitability to study the solvation properties of an interesting encounter complex, barnase-barstar. The promising results suggest that coarse-graining the protein with the MARTINI force field is indeed a valuable step to broaden VISM's and MARTINI's applications in the near future.

Self-assembled micro-organogels for 3D printing silicone structures

PubMed Central

O’Bryan, Christopher S.; Bhattacharjee, Tapomoy; Hart, Samuel; Kabb, Christopher P.; Schulze, Kyle D.; Chilakala, Indrasena; Sumerlin, Brent S.; Sawyer, W. Gregory; Angelini, Thomas E.

2017-01-01

The widespread prevalence of commercial products made from microgels illustrates the immense practical value of harnessing the jamming transition; there are countless ways to use soft, solid materials that fluidize and become solid again with small variations in applied stress. The traditional routes of microgel synthesis produce materials that predominantly swell in aqueous solvents or, less often, in aggressive organic solvents, constraining ways that these exceptionally useful materials can be used. For example, aqueous microgels have been used as the foundation of three-dimensional (3D) bioprinting applications, yet the incompatibility of available microgels with nonpolar liquids, such as oils, limits their use in 3D printing with oil-based materials, such as silicone. We present a method to make micro-organogels swollen in mineral oil, using block copolymer self-assembly. The rheological properties of this micro-organogel material can be tuned, leveraging the jamming transition to facilitate its use in 3D printing of silicone structures. We find that the minimum printed feature size can be controlled by the yield stress of the micro-organogel medium, enabling the fabrication of numerous complex silicone structures, including branched perfusable networks and functional fluid pumps. PMID:28508071

Shape-designed single-polymer micelles: a proof-of-concept simulation

NASA Astrophysics Data System (ADS)

Moths, Brian; Witten, Thomas A.

Much effort has been directed towards self-assembling nanostructures. Strong, local interactions between specific building blocks often determine these structures (e.g., globular proteins). We seek to produce designed structures that are instead determined by collective effects of weak interactions (e.g., surfactant self-assembly). Such structures may reversibly change conformation or disassemble in response to changing solvent conditions, and, being soft, have potential to adapt to fluctuating or unknown application-imposed shape requirements. Concretely, we aim to realize such a structure in the form of a single polymer micelle--an amphiphilic polymer exhibiting a condensed, phase-segregated conformation when immersed in solvent. Connecting all amphiphiles into a single chain provides geometric constraints controlling the surface curvature profile, thus dictating a non-trivial shape. We present 2D Monte Carlo simulation results demonstrating the feasibility of such soft, shape-designed micelles. Preliminary results demonstrate a stable concave ``dimple'' in a micelle composed of a single A-B multiblock linear copolymer. We discuss both current limitations on shape robustness and effects of block asymmetry, block molecular weights and overall chain length on micelle shape. This work was supported in part by the National Science Foundation's MRSEC Program under Award Number DMR-1420709.

Structural Transformation of Diblock Copolymer/Homopolymer Assemblies by Tuning Cylindrical Confinement and Interfacial Interactions.

PubMed

Xu, Jiangping; Wang, Ke; Liang, Ruijing; Yang, Yi; Zhou, Huamin; Xie, Xiaolin; Zhu, Jintao

2015-11-17

In this study, we report the controllable structural transformation of block copolymer/homopolymer binary blends in cylindrical nanopores. Polystyrene-b-poly(4-vinylpyridine)/homopolystyrene (SVP/hPS) nanorods (NRs) can be fabricated by pouring the polymers into an anodic aluminum oxide (AAO) channel and isolated by selective removal of the AAO membrane. In this two-dimensional (2D) confinement, SVP self-assembles into NRs with concentric lamellar structure, and the internal structure can be tailored with the addition of hPS. We show that the weight fraction and molecular weight of hPS and the diameter of the channels can significantly affect the internal structure of the NRs. Moreover, mesoporous materials with tunable pore shape, size, and packing style can be prepared by selective solvent swelling of the structured NRs. In addition, these NRs can transform into spherical structures through solvent-absorption annealing, triggering the conversion from 2D to 3D confinement. More importantly, the transformation dynamics can be tuned by varying the preference property of surfactant to the polymers. It is proven that the shape and internal structure of the polymer particles are dominated by the interfacial interactions governed by the surfactants.

Directed self-assembly of high-chi block copolymer for nano fabrication of bit patterned media via solvent annealing

NASA Astrophysics Data System (ADS)

Xiong, Shisheng; Chapuis, Yves-Andre; Wan, Lei; Gao, He; Li, Xiao; Ruiz, Ricardo; Nealey, Paul F.

2016-10-01

We report the formation of nanoimprint master templates that can be used for the fabrication of bit patterned media (BPM). The template was formed by directed self-assembly, with solvent annealing, of a symmetric ABA triblock copolymer to form perpendicularly oriented lamellae on chemical patterns. We used a high-χ block copolymer, poly(2-vinyl pyridine)-block-polystyrene-block-poly(2-vinyl pyridine) to achieve smaller feature sizes than are possible with polystyrene-block-poly(methyl methacrylate). The work shows that triblock copolymers can provide a large processing window in terms of pitch commensurability. Using block-selective infiltration (atomic layer deposition with sequential long soaking/purge cycles), an alumina composite with high etch resistance was specifically incorporated into the polar and hydrophilic P2VP domains. Subsequently, the surface pattern was successfully transferred into underlying Si substrates by etching with a fluorine-containing plasma to create a nanoimprint master. The line/space pattern of the nanoimprint master met the BPM fabrication requirement of defectivity <10-3. For demonstration purposes, the nanoimprint master was used to imprint a replica pattern of photoresist on a quartz wafer.

Morphological Evolution of Block Copolymer Particles: Effect of Solvent Evaporation Rate on Particle Shape and Morphology.

PubMed

Shin, Jae Man; Kim, YongJoo; Yun, Hongseok; Yi, Gi-Ra; Kim, Bumjoon J

2017-02-28

Shape and morphology of polymeric particles are of great importance in controlling their optical properties or self-assembly into unusual superstructures. Confinement of block copolymers (BCPs) in evaporative emulsions affords particles with diverse structures, including prolate ellipsoids, onion-like spheres, oblate ellipsoids, and others. Herein, we report that the evaporation rate of solvent from emulsions encapsulating symmetric polystyrene-b-polybutadiene (PS-b-PB) determines the shape and internal nanostructure of micron-sized BCP particles. A distinct morphological transition from the ellipsoids with striped lamellae to the onion-like spheres was observed with decreasing evaporation rate. Experiments and dissipative particle dynamics (DPD) simulations showed that the evaporation rate affected the organization of BCPs at the particle surface, which determined the final shape and internal nanostructure of the particles. Differences in the solvent diffusion rates in PS and PB at rapid evaporation rates induced alignment of both domains perpendicular to the particle surface, resulting in ellipsoids with axial lamellar stripes. Slower evaporation rates provided sufficient time for BCP organization into onion-like structures with PB as the outermost layer, owing to the preferential interaction of PB with the surroundings. BCP molecular weight was found to influence the critical evaporation rate corresponding to the morphological transition from ellipsoid to onion-like particles, as well as the ellipsoid aspect ratio. DPD simulations produced morphologies similar to those obtained from experiments and thus elucidated the mechanism and driving forces responsible for the evaporation-induced assembly of BCPs into particles with well-defined shapes and morphologies.

Direct Immersion Annealing of Thin Block Copolymer Films.

PubMed

Modi, Arvind; Bhaway, Sarang M; Vogt, Bryan D; Douglas, Jack F; Al-Enizi, Abdullah; Elzatahry, Ahmed; Sharma, Ashutosh; Karim, Alamgir

2015-10-07

We demonstrate ordering of thin block copolymer (BCP) films via direct immersion annealing (DIA) at enhanced rate leading to stable morphologies. The BCP films are immersed in carefully selected mixtures of good and marginal solvents that can impart enhanced polymer mobility, while inhibiting film dissolution. DIA is compatible with roll-to-roll assembly manufacturing and has distinct advantages over conventional thermal annealing and batch processing solvent-vapor annealing methods. We identify three solvent composition-dependent BCP film ordering regimes in DIA for the weakly interacting polystyrene-poly(methyl methacrylate) (PS-PMMA) system: rapid short-range order, optimal long-range order, and a film instability regime. Kinetic studies in the "optimal long-range order" processing regime as a function of temperature indicate a significant reduction of activation energy for BCP grain growth compared to oven annealing at conventional temperatures. An attractive feature of DIA is its robustness to ordering other BCP (e.g. PS-P2VP) and PS-PMMA systems exhibiting spherical, lamellar and cylindrical ordering.

Solvent immersion imprint lithography: A high-performance, semi-automated procedure

PubMed Central

Liyu, D. A.; Canul, A. J.; Vasdekis, A. E.

2017-01-01

We expand upon our recent, fundamental report on solvent immersion imprint lithography (SIIL) and describe a semi-automated and high-performance procedure for prototyping polymer microfluidics and optofluidics. The SIIL procedure minimizes manual intervention through a cost-effective (∼$200) and easy-to-assemble apparatus. We analyze the procedure's performance specifically for Poly (methyl methacrylate) microsystems and report repeatable polymer imprinting, bonding, and 3D functionalization in less than 5 min, down to 8 μm resolutions and 1:1 aspect ratios. In comparison to commercial approaches, the modified SIIL procedure enables substantial cost reductions, a 100-fold reduction in imprinting force requirements, as well as a more than 10-fold increase in bonding strength. We attribute these advantages to the directed polymer dissolution that strictly localizes at the polymer-solvent interface, as uniquely offered by SIIL. The described procedure opens new desktop prototyping opportunities, particularly for non-expert users performing live-cell imaging, flow-through catalysis, and on-chip gas detection. PMID:28798847

Direct Immersion Annealing of Thin Block Copolymer Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Modi, Arvind; Bhaway, Sarang M.; Vogt, Bryan D.

2015-09-09

We demonstrate ordering of thin block copolymer (BCP) films via direct immersion annealing (DIA) at enhanced rate leading to stable morphologies. The BCP films are immersed in carefully selected mixtures of good and marginal solvents that can impart enhanced polymer mobility, while inhibiting film dissolution. DIA is compatible with roll-to-roll assembly manufacturing and has distinct advantages over conventional thermal annealing and batch processing solvent-vapor annealing methods. We identify three solvent composition-dependent BCP film ordering regimes in DIA for the weakly interacting polystyrene–poly(methyl methacrylate) (PS–PMMA) system: rapid short-range order, optimal long-range order, and a film instability regime. Kinetic studies in themore » “optimal long-range order” processing regime as a function of temperature indicate a significant reduction of activation energy for BCP grain growth compared to oven annealing at conventional temperatures. An attractive feature of DIA is its robustness to ordering other BCP (e.g. PS-P2VP) and PS-PMMA systems exhibiting spherical, lamellar and cylindrical ordering.« less

IMPORTANCE OF ENZYMATIC BIOTRANSFORMATION IN IMMUNOTOXICOLOGY

EPA Science Inventory

Many immunotoxic compounds, such as benzene and other organic solvents, pesticides, mycotoxins and polycyclic aromatic hydrocarbons, can alter immune function only after undergoing enzyme-mediated reactions within various tissues. In the review that follows, the role of enzymatic...

Modeling solid-state transformations occurring in dissolution testing.

PubMed

Laaksonen, Timo; Aaltonen, Jaakko

2013-04-15

Changes in the solid-state form can occur during dissolution testing of drugs. This can often complicate interpretation of results. Additionally, there can be several mechanisms through which such a change proceeds, e.g. solvent-mediated transformation or crystal growth within the drug material itself. Here, a mathematical model was constructed to study the dissolution testing of a material, which undergoes such changes. The model consisted of two processes: the recrystallization of the drug from a supersaturated liquid state caused by the dissolution of the more soluble solid form and the crystal growth of the stable solid form at the surface of the drug formulation. Comparison to experimental data on theophylline dissolution showed that the results obtained with the model matched real solid-state changes and that it was able to distinguish between cases where the transformation was controlled either by solvent-mediated crystallization or solid-state crystal growth. Copyright © 2013 Elsevier B.V. All rights reserved.

Self-Assembly, Surface Activity and Structure of n-Octyl-β-D-thioglucopyranoside in Ethylene Glycol-Water Mixtures

PubMed Central

Ruiz, Cristóbal Carnero; Molina-Bolívar, José Antonio; Hierrezuelo, José Manuel; Liger, Esperanza

2013-01-01

The effect of the addition of ethylene glycol (EG) on the interfacial adsorption and micellar properties of the alkylglucoside surfactant n-octyl-β-d-thioglucopyranoside (OTG) has been investigated. Critical micelle concentrations (cmc) upon EG addition were obtained by both surface tension measurements and the pyrene 1:3 ratio method. A systematic increase in the cmc induced by the presence of the co-solvent was observed. This behavior was attributed to a reduction in the cohesive energy of the mixed solvent with respect to pure water, which favors an increase in the solubility of the surfactant with EG content. Static light scattering measurements revealed a decrease in the mean aggregation number of the OTG micelles with EG addition. Moreover, dynamic light scattering data showed that the effect of the surfactant concentration on micellar size is also controlled by the content of the co-solvent in the system. Finally, the effect of EG addition on the microstructure of OTG micelles was investigated using the hydrophobic probe Coumarin 153 (C153). Time-resolved fluorescence anisotropy decay curves of the probe solubilized in micelles were analyzed using the two-step model. The results indicate a slight reduction of the average reorientation time of the probe molecule with increasing EG in the mixed solvent system, thereby suggesting a lesser compactness induced by the presence of the co-solvent. PMID:23385232

Self-assembly, surface activity and structure of n-octyl-β-D-thioglucopyranoside in ethylene glycol-water mixtures.

PubMed

Ruiz, Cristóbal Carnero; Molina-Bolívar, José Antonio; Hierrezuelo, José Manuel; Liger, Esperanza

2013-02-05

The effect of the addition of ethylene glycol (EG) on the interfacial adsorption and micellar properties of the alkylglucoside surfactant n-octyl-β-D-thioglucopyranoside (OTG) has been investigated. Critical micelle concentrations (cmc) upon EG addition were obtained by both surface tension measurements and the pyrene 1:3 ratio method. A systematic increase in the cmc induced by the presence of the co-solvent was observed. This behavior was attributed to a reduction in the cohesive energy of the mixed solvent with respect to pure water, which favors an increase in the solubility of the surfactant with EG content. Static light scattering measurements revealed a decrease in the mean aggregation number of the OTG micelles with EG addition. Moreover, dynamic light scattering data showed that the effect of the surfactant concentration on micellar size is also controlled by the content of the co-solvent in the system. Finally, the effect of EG addition on the microstructure of OTG micelles was investigated using the hydrophobic probe Coumarin 153 (C153). Time-resolved fluorescence anisotropy decay curves of the probe solubilized in micelles were analyzed using the two-step model. The results indicate a slight reduction of the average reorientation time of the probe molecule with increasing EG in the mixed solvent system, thereby suggesting a lesser compactness induced by the presence of the co-solvent.

Morphological transformations of diblock copolymers in binary solvents: A simulation study

NASA Astrophysics Data System (ADS)

Wang, Zheng; Yin, Yuhua; Jiang, Run; Li, Baohui

2017-12-01

Morphological transformations of amphiphilic AB diblock copolymers in mixtures of a common solvent (S1) and a selective solvent (S2) for the B block are studied using the simulated annealing method. We focus on the morphological transformation depending on the fraction of the selective solvent C S2, the concentration of the polymer C p , and the polymer-solvent interactions ɛ ij ( i = A, B; j = S1, S2). Morphology diagrams are constructed as functions of C p , C S2, and/or ɛ AS2. The copolymer morphological sequence from dissolved → sphere → rod → ring/cage → vesicle is obtained upon increasing C S2 at a fixed C p . This morphology sequence is consistent with previous experimental observations. It is found that the selectivity of the selective solvent affects the self-assembled microstructure significantly. In particular, when the interaction ɛ BS2 is negative, aggregates of stacked lamellae dominate the diagram. The mechanisms of aggregate transformation and the formation of stacked lamellar aggregates are discussed by analyzing variations of the average contact numbers of the A or B monomers with monomers and with molecules of the two types of solvent, as well as the mean square end-to-end distances of chains. It is found that the basic morphological sequence of spheres to rods to vesicles and the stacked lamellar aggregates result from competition between the interfacial energy and the chain conformational entropy. Analysis of the vesicle structure reveals that the vesicle size increases with increasing C p or with decreasing C S2, but remains almost unchanged with variations in ɛ AS2.

Chemical reactions directed Peptide self-assembly.

PubMed

Rasale, Dnyaneshwar B; Das, Apurba K

2015-05-13

Fabrication of self-assembled nanostructures is one of the important aspects in nanoscience and nanotechnology. The study of self-assembled soft materials remains an area of interest due to their potential applications in biomedicine. The versatile properties of soft materials can be tuned using a bottom up approach of small molecules. Peptide based self-assembly has significant impact in biology because of its unique features such as biocompatibility, straight peptide chain and the presence of different side chain functionality. These unique features explore peptides in various self-assembly process. In this review, we briefly introduce chemical reaction-mediated peptide self-assembly. Herein, we have emphasised enzymes, native chemical ligation and photochemical reactions in the exploration of peptide self-assembly.

Chemical Reactions Directed Peptide Self-Assembly

PubMed Central

Rasale, Dnyaneshwar B.; Das, Apurba K.

2015-01-01

Fabrication of self-assembled nanostructures is one of the important aspects in nanoscience and nanotechnology. The study of self-assembled soft materials remains an area of interest due to their potential applications in biomedicine. The versatile properties of soft materials can be tuned using a bottom up approach of small molecules. Peptide based self-assembly has significant impact in biology because of its unique features such as biocompatibility, straight peptide chain and the presence of different side chain functionality. These unique features explore peptides in various self-assembly process. In this review, we briefly introduce chemical reaction-mediated peptide self-assembly. Herein, we have emphasised enzymes, native chemical ligation and photochemical reactions in the exploration of peptide self-assembly. PMID:25984603

Ionic Liquids Can Selectively Change the Conformational Free-Energy Landscape of Sugar Rings.

PubMed

Jarin, Zack; Pfaendtner, Jim

2014-02-11

We investigated the conformational free energy landscape of glucose solvated in water and in the ionic liquids (ILs) 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) and 1-butyl-3-methylimidazoulim boron tetrafluoride ([Bmim][BF4]). To quantify equilibrium thermodynamic solvent effects, molecular dynamics simulations in conjunction with enhanced sampling based on the metadynamics framework were used. The results show that the solvent choice induces significant differences in the equilibrium ring structures, which may help further resolve the molecular mechanism governing IL-mediated cellulose dissolution.

Solvothermal synthesis and controlled self-assembly of monodisperse titanium-based perovskite colloidal nanocrystals

NASA Astrophysics Data System (ADS)

Caruntu, Daniela; Rostamzadeh, Taha; Costanzo, Tommaso; Salemizadeh Parizi, Saman; Caruntu, Gabriel

2015-07-01

The rational design of monodisperse ferroelectric nanocrystals with controlled size and shape and their organization into hierarchical structures has been a critical step for understanding the polar ordering in nanoscale ferroelectrics, as well as the design of nanocrystal-based functional materials which harness the properties of individual nanoparticles and the collective interactions between them. We report here on the synthesis and self-assembly of aggregate-free, single-crystalline titanium-based perovskite nanoparticles with controlled morphology and surface composition by using a simple, easily scalable and highly versatile colloidal route. Single-crystalline, non-aggregated BaTiO3 colloidal nanocrystals, used as a model system, have been prepared under solvothermal conditions at temperatures as low as 180 °C. The shape of the nanocrystals was tuned from spheroidal to cubic upon changing the polarity of the solvent, whereas their size was varied from 16 to 30 nm for spheres and 5 to 78 nm for cubes by changing the concentration of the precursors and the reaction time, respectively. The hydrophobic, oleic acid-passivated nanoparticles exhibit very good solubility in non-polar solvents and can be rendered dispersible in polar solvents by a simple process involving the oxidative cleavage of the double bond upon treating the nanopowders with the Lemieux-von Rudloff reagent. Lattice dynamic analysis indicated that regardless of their size, BaTiO3 nanocrystals present local disorder within the perovskite unit cell, associated with the existence of polar ordering. We also demonstrate for the first time that, in addition to being used for fabricating large area, crack-free, highly uniform films, BaTiO3 nanocubes can serve as building blocks for the design of 2D and 3D mesoscale structures, such as superlattices and superparticles. Interestingly, the type of superlattice structure (simple cubic or face centered cubic) appears to be determined by the type of solvent in which the nanocrystals were dispersed. This approach provides an excellent platform for the synthesis of other titanium-based perovskite colloidal nanocrystals with controlled chemical composition, surface structure and morphology and for their assembly into complex architectures, therefore opening the door for the design of novel mesoscale functional materials/nanocomposites with potential applications in energy conversion, data storage and the biomedical field.The rational design of monodisperse ferroelectric nanocrystals with controlled size and shape and their organization into hierarchical structures has been a critical step for understanding the polar ordering in nanoscale ferroelectrics, as well as the design of nanocrystal-based functional materials which harness the properties of individual nanoparticles and the collective interactions between them. We report here on the synthesis and self-assembly of aggregate-free, single-crystalline titanium-based perovskite nanoparticles with controlled morphology and surface composition by using a simple, easily scalable and highly versatile colloidal route. Single-crystalline, non-aggregated BaTiO3 colloidal nanocrystals, used as a model system, have been prepared under solvothermal conditions at temperatures as low as 180 °C. The shape of the nanocrystals was tuned from spheroidal to cubic upon changing the polarity of the solvent, whereas their size was varied from 16 to 30 nm for spheres and 5 to 78 nm for cubes by changing the concentration of the precursors and the reaction time, respectively. The hydrophobic, oleic acid-passivated nanoparticles exhibit very good solubility in non-polar solvents and can be rendered dispersible in polar solvents by a simple process involving the oxidative cleavage of the double bond upon treating the nanopowders with the Lemieux-von Rudloff reagent. Lattice dynamic analysis indicated that regardless of their size, BaTiO3 nanocrystals present local disorder within the perovskite unit cell, associated with the existence of polar ordering. We also demonstrate for the first time that, in addition to being used for fabricating large area, crack-free, highly uniform films, BaTiO3 nanocubes can serve as building blocks for the design of 2D and 3D mesoscale structures, such as superlattices and superparticles. Interestingly, the type of superlattice structure (simple cubic or face centered cubic) appears to be determined by the type of solvent in which the nanocrystals were dispersed. This approach provides an excellent platform for the synthesis of other titanium-based perovskite colloidal nanocrystals with controlled chemical composition, surface structure and morphology and for their assembly into complex architectures, therefore opening the door for the design of novel mesoscale functional materials/nanocomposites with potential applications in energy conversion, data storage and the biomedical field. Electronic supplementary information (ESI) available: FE-SEM image of 12 nm BaTiO3 nanocubes deposited onto a silicon wafer (Fig. SI1), the X-ray diffraction pattern of a superlattice structure formed by monodisperse 10 nm BaTiO3 cuboidal nanocrystals (Fig. SI2) and TEM images of a BaTiO3 superparticle (Fig. SI3). See DOI: 10.1039/c5nr00737b

Role of translational entropy in spatially inhomogeneous, coarse-grained models

NASA Astrophysics Data System (ADS)

Langenberg, Marcel; Jackson, Nicholas E.; de Pablo, Juan J.; Müller, Marcus

2018-03-01

Coarse-grained models of polymer and biomolecular systems have enabled the computational study of cooperative phenomena, e.g., self-assembly, by lumping multiple atomistic degrees of freedom along the backbone of a polymer, lipid, or DNA molecule into one effective coarse-grained interaction center. Such a coarse-graining strategy leaves the number of molecules unaltered. In order to treat the surrounding solvent or counterions on the same coarse-grained level of description, one can also stochastically group several of those small molecules into an effective, coarse-grained solvent bead or "fluid element." Such a procedure reduces the number of molecules, and we discuss how to compensate the concomitant loss of translational entropy by density-dependent interactions in spatially inhomogeneous systems.

Surfactant Behavior of Sodium Dodecylsulfate in Deep Eutectic Solvent Choline Chloride/Urea.

PubMed

Arnold, T; Jackson, A J; Sanchez-Fernandez, A; Magnone, D; Terry, A E; Edler, K J

2015-12-01

Deep eutectic solvents (DES) resemble ionic liquids but are formed from an ionic mixture instead of being a single ionic compound. Here we present some results that demonstrate that surfactant sodium dodecyl sulfate (SDS) remains surface-active and shows self-assembly phenomena in the most commonly studied DES, choline chloride/urea. X-ray reflectivity (XRR) and small angle neutron scattering (SANS) suggest that the behavior is significantly different from that in water. Our SANS data supports our determination of the critical micelle concentration using surface-tension measurements and suggests that the micelles formed in DES do not have the same shape and size as those seen in water. Reflectivity measurements have also demonstrated that the surfactants remain surface-active below this concentration.

Method for making surfactant-templated thin films

DOEpatents

Brinker, C. Jeffrey; Lu, Yunfeng; Fan, Hong You

2010-08-31

An evaporation-induced self-assembly method to prepare a porous, surfactant-templated, thin film by mixing a silica sol, a solvent, a surfactant, and an interstitial compound, evaporating a portion of the solvent to form a liquid, crystalline thin film mesophase material, and then removal of the surfactant template. Coating onto a substrate produces a thin film with the interstitial compound either covalently bonded to the internal surfaces of the ordered or disordered mesostructure framework or physically entrapped within the ordered or disordered mesostructured framework. Particles can be formed by aerosol processing or spray drying rather than coating onto a substrate. The selection of the interstitial compound provides a means for developing thin films for applications including membranes, sensors, low dielectric constant films, photonic materials and optical hosts.

Method for making surfactant-templated thin films

DOEpatents

Brinker, C. Jeffrey; Lu, Yunfeng; Fan, Hongyou

2002-01-01

An evaporation-induced self-assembly method to prepare a porous, surfactant-templated, thin film by mixing a silica sol, a solvent, a surfactant, and an interstitial compound, evaporating a portion of the solvent to form a liquid, crystalline thin film mesophase material, and then removal of the surfactant template. Coating onto a substrate produces a thin film with the interstitial compound either covalently bonded to the internal surfaces of the ordered or disordered mesostructure framework or physically entrapped within the ordered or disordered mesostructured framework. Particles can be formed by aerosol processing or spray drying rather than coating onto a substrate. The selection of the interstitial compound provides a means for developing thin films for applications including membranes, sensors, low dielectric constant films, photonic materials and optical hosts.

Assembly of Customized TAL Effectors Through Advanced ULtiMATE System.

PubMed

Yang, Junjiao; Guo, Shengjie; Yuan, Pengfei; Wei, Wensheng

2016-01-01

Transcription activator-like effectors (TALEs) have been widely applied in gene targeting. Here we describe an advanced ULtiMATE (USER-based Ligation-Mediated Assembly of TAL Effector) system that utilizes USER fusion technique and archive of 512 tetramer templates to achieve highly efficient construction of TALEs, which takes only half a day to accomplish the assembly of any given TALE construct. This system is also suitable for large-scale assembly of TALENs and any other TALE-based constructions.

Green-fuel-mediated synthesis of self-assembled NiO nano-sticks for dual applications—photocatalytic activity on Rose Bengal dye and antimicrobial action on bacterial strains

NASA Astrophysics Data System (ADS)

Iyyappa Rajan, P.; Vijaya, J. Judith; Jesudoss, S. K.; Kaviyarasu, K.; Kennedy, L. John; Jothiramalingam, R.; Al-Lohedan, Hamad A.; Vaali-Mohammed, Mansoor-Ali

2017-08-01

With aim of promoting the employability of green fuels in the synthesis of nano-scaled materials with new kinds of morphologies for multiple applications, successful synthesis of self-assembled NiO nano-sticks was achieved through a 100% green-fuel-mediated hot-plate combustion reaction. The synthesized NiO nano-sticks show excellent photocatalytic activity on Rose Bengal dye and superior antibacterial potential towards both Gram-positive and Gram-negative bacteria.

Mechanisms of solvent resistance mediated by interplay of cellular factors in Pseudomonas putida.

PubMed

Ramos, Juan-Luis; Sol Cuenca, Maria; Molina-Santiago, Carlos; Segura, Ana; Duque, Estrella; Gómez-García, María R; Udaondo, Zulema; Roca, Amalia

2015-07-01

A number of microorganisms have the ability to thrive in the presence of a range of toxic solvents. Tolerance to these chemicals is a multifactorial process, meaning that bacterial cells use a set of physiological and gene expression changes to overcome the damage imparted by these chemicals. This review focuses mainly on issues related to tolerance to aromatic hydrocarbons and butanol in Pseudomonas, although other microorganisms are also discussed. Pseudomonas putida strains contain a circular chromosome of approximately 6 Mbp which encodes about 5300 genes. A combination of physiological and biochemical assays, a genome-wide collection of mutants and several omics approaches have provided useful information to help identify functions involved in solvent tolerance in P. putida. The solvent response involves fine-tuning of lipid fluidity to adjust membrane functions including impermeabilization, activation of a general stress-response system, increased energy generation and induction of specific efflux pumps that extrude solvents to the medium. These responses are modulated at the transcriptional level by local and global regulators as well as by a number of sRNAs whose levels fluctuate with the presence of solvents in the environment. Taken as a whole these regulatory inputs orchestrate the complex network of metabolic responses observed after solvent addition. © FEMS 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Controlled ionic condensation at the surface of a native extremophile membrane

NASA Astrophysics Data System (ADS)

Contera, Sonia Antoranz; Voïtchovsky, Kislon; Ryan, John F.

2010-02-01

At the nanoscale level biological membranes present a complex interface with the solvent. The functional dynamics and relative flexibility of membrane components together with the presence of specific ionic effects can combine to create exciting new phenomena that challenge traditional theories such as the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory or models interpreting the role of ions in terms of their ability to structure water (structure making/breaking). Here we investigate ionic effects at the surface of a highly charged extremophile membrane composed of a proton pump (bacteriorhodopsin) and archaeal lipids naturally assembled into a 2D crystal. Using amplitude-modulation atomic force microscopy (AM-AFM) in solution, we obtained sub-molecular resolution images of ion-induced surface restructuring of the membrane. We demonstrate the presence of a stiff cationic layer condensed at its extracellular surface. This layer cannot be explained by traditional continuum theories. Dynamic force spectroscopy experiments suggest that it is produced by electrostatic correlation mediated by a Manning-type condensation of ions. In contrast, the cytoplasmic surface is dominated by short-range repulsive hydration forces. These findings are relevant to archaeal bioenergetics and halophilic adaptation. Importantly, they present experimental evidence of a natural system that locally controls its interactions with the surrounding medium and challenges our current understanding of biological interfaces.At the nanoscale level biological membranes present a complex interface with the solvent. The functional dynamics and relative flexibility of membrane components together with the presence of specific ionic effects can combine to create exciting new phenomena that challenge traditional theories such as the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory or models interpreting the role of ions in terms of their ability to structure water (structure making/breaking). Here we investigate ionic effects at the surface of a highly charged extremophile membrane composed of a proton pump (bacteriorhodopsin) and archaeal lipids naturally assembled into a 2D crystal. Using amplitude-modulation atomic force microscopy (AM-AFM) in solution, we obtained sub-molecular resolution images of ion-induced surface restructuring of the membrane. We demonstrate the presence of a stiff cationic layer condensed at its extracellular surface. This layer cannot be explained by traditional continuum theories. Dynamic force spectroscopy experiments suggest that it is produced by electrostatic correlation mediated by a Manning-type condensation of ions. In contrast, the cytoplasmic surface is dominated by short-range repulsive hydration forces. These findings are relevant to archaeal bioenergetics and halophilic adaptation. Importantly, they present experimental evidence of a natural system that locally controls its interactions with the surrounding medium and challenges our current understanding of biological interfaces. Electronic supplementary information (ESI) available: Figs. S1 and S2: amplitude- and phase-extension curves used to derive the data presented in Figs. 2 and 4. See DOI: 10.1039/b9nr00248k

Mediator independently orchestrates multiple steps of preinitiation complex assembly in vivo

PubMed Central

Eyboulet, Fanny; Wydau-Dematteis, Sandra; Eychenne, Thomas; Alibert, Olivier; Neil, Helen; Boschiero, Claire; Nevers, Marie-Claire; Volland, Hervé; Cornu, David; Redeker, Virginie; Werner, Michel; Soutourina, Julie

2015-01-01

Mediator is a large multiprotein complex conserved in all eukaryotes, which has a crucial coregulator function in transcription by RNA polymerase II (Pol II). However, the molecular mechanisms of its action in vivo remain to be understood. Med17 is an essential and central component of the Mediator head module. In this work, we utilised our large collection of conditional temperature-sensitive med17 mutants to investigate Mediator's role in coordinating preinitiation complex (PIC) formation in vivo at the genome level after a transfer to a non-permissive temperature for 45 minutes. The effect of a yeast mutation proposed to be equivalent to the human Med17-L371P responsible for infantile cerebral atrophy was also analyzed. The ChIP-seq results demonstrate that med17 mutations differentially affected the global presence of several PIC components including Mediator, TBP, TFIIH modules and Pol II. Our data show that Mediator stabilizes TFIIK kinase and TFIIH core modules independently, suggesting that the recruitment or the stability of TFIIH modules is regulated independently on yeast genome. We demonstrate that Mediator selectively contributes to TBP recruitment or stabilization to chromatin. This study provides an extensive genome-wide view of Mediator's role in PIC formation, suggesting that Mediator coordinates multiple steps of a PIC assembly pathway. PMID:26240385

Functionalization of quantum rods with oligonucleotides for programmable assembly with DNA origami

NASA Astrophysics Data System (ADS)

Doane, Tennyson L.; Alam, Rabeka; Maye, Mathew M.

2015-02-01

The DNA-mediated self-assembly of CdSe/CdS quantum rods (QRs) onto DNA origami is described. Two QR types with unique optical emission and high polarization were synthesized, and then functionalized with oligonucleotides (ssDNA) using a novel protection-deprotection approach, which harnessed ssDNA's tailorable rigidity and denaturation temperature to increase DNA coverage by reducing non-specific coordination and wrapping. The QR assembly was programmable, and occurred at two different assembly zones that had capture strands in parallel alignment. QRs with different optical properties were assembled, opening up future studies on orientation dependent QR FRET. The QR-origami conjugates could be purified via gel electrophoresis and sucrose gradient ultracentrifugation. Assembly yields, QR stoichiometry and orientation, as well as energy transfer implications were studied in light of QR distances, origami flexibility, and conditions.The DNA-mediated self-assembly of CdSe/CdS quantum rods (QRs) onto DNA origami is described. Two QR types with unique optical emission and high polarization were synthesized, and then functionalized with oligonucleotides (ssDNA) using a novel protection-deprotection approach, which harnessed ssDNA's tailorable rigidity and denaturation temperature to increase DNA coverage by reducing non-specific coordination and wrapping. The QR assembly was programmable, and occurred at two different assembly zones that had capture strands in parallel alignment. QRs with different optical properties were assembled, opening up future studies on orientation dependent QR FRET. The QR-origami conjugates could be purified via gel electrophoresis and sucrose gradient ultracentrifugation. Assembly yields, QR stoichiometry and orientation, as well as energy transfer implications were studied in light of QR distances, origami flexibility, and conditions. Electronic supplementary information (ESI) available: Experimental conditions, DNA origami blueprint and sequences, FRET calculations. Additional Fig. S1-S13. See DOI: 10.1039/c4nr07662a

BLNK: molecular scaffolding through ‘cis’-mediated organization of signaling proteins

PubMed Central

Chiu, Christopher W.; Dalton, Mark; Ishiai, Masamichi; Kurosaki, Tomohiro; Chan, Andrew C.

2002-01-01

Assembly of intracellular macromolecular complexes is thought to provide an important mechanism to coordinate the generation of second messengers upon receptor activation. We have previously identified a B cell linker protein, termed BLNK, which serves such a scaffolding function in B cells. We demonstrate here that phosphorylation of five tyrosine residues within human BLNK nucleates distinct signaling effectors following B cell antigen receptor activation. The phosphorylation of multiple tyrosine residues not only amplifies PLCγ-mediated signaling but also supports ‘cis’-mediated interaction between distinct signaling effectors within a large molecular complex. These data demonstrate the importance of coordinate phosphorylation of molecular scaffolds, and provide insights into how assembly of macromolecular complexes is required for normal receptor function. PMID:12456653

Theoretical study of solvent effects on the coil-globule transition

NASA Astrophysics Data System (ADS)

Polson, James M.; Opps, Sheldon B.; Abou Risk, Nicholas

2009-06-01

The coil-globule transition of a polymer in a solvent has been studied using Monte Carlo simulations of a single chain subject to intramolecular interactions as well as a solvent-mediated effective potential. This solvation potential was calculated using several different theoretical approaches for two simple polymer/solvent models, each employing hard-sphere chains and hard-sphere solvent particles as well as attractive square-well potentials between some interaction sites. For each model, collapse is driven by variation in a parameter which changes the energy mismatch between monomers and solvent particles. The solvation potentials were calculated using two fundamentally different methodologies, each designed to predict the conformational behavior of polymers in solution: (1) the polymer reference interaction site model (PRISM) theory and (2) a many-body solvation potential (MBSP) based on scaled particle theory introduced by Grayce [J. Chem. Phys. 106, 5171 (1997)]. For the PRISM calculations, two well-studied solvation monomer-monomer pair potentials were employed, each distinguished by the closure relation used in its derivation: (i) a hypernetted-chain (HNC)-type potential and (ii) a Percus-Yevick (PY)-type potential. The theoretical predictions were each compared to results obtained from explicit-solvent discontinuous molecular dynamics simulations on the same polymer/solvent model systems [J. Chem. Phys. 125, 194904 (2006)]. In each case, the variation in the coil-globule transition properties with solvent density is mostly qualitatively correct, though the quantitative agreement between the theory and prediction is typically poor. The HNC-type potential yields results that are more qualitatively consistent with simulation. The conformational behavior of the polymer upon collapse predicted by the MBSP approach is quantitatively correct for low and moderate solvent densities but is increasingly less accurate for higher densities. At high solvent densities, the PRISM-HNC and MBSP approaches tend to overestimate, while the PRISM-PY approach underestimates the tendency of the solvent to drive polymer collapse.

Large-area fluidic assembly of single-walled carbon nanotubes through dip-coating and directional evaporation

NASA Astrophysics Data System (ADS)

Kim, Pilnam; Kang, Tae June

2017-12-01

We present a simple and scalable fluidic-assembly approach, in which bundles of single-walled carbon nanotubes (SWCNTs) are selectively aligned and deposited by directionally controlled dip-coating and solvent evaporation processes. The patterned surface with alternating regions of hydrophobic polydimethyl siloxane (PDMS) (height 100 nm) strips and hydrophilic SiO2 substrate was withdrawn vertically at a constant speed ( 3 mm/min) from a solution bath containing SWCNTs ( 0.1 mg/ml), allowing for directional evaporation and subsequent selective deposition of nanotube bundles along the edges of horizontally aligned PDMS strips. In addition, the fluidic assembly was applied to fabricate a field effect transistor (FET) with highly oriented SWCNTs, which demonstrate significantly higher current density as well as high turn-off ratio (T/O ratio 100) as compared to that with randomly distributed carbon nanotube bundles (T/O ratio <10).

Asymmetric organic-inorganic hybrid membrane formation via block copolymer-nanoparticle co-assembly.

PubMed

Gu, Yibei; Dorin, Rachel M; Wiesner, Ulrich

2013-01-01

A facile method for forming asymmetric organic-inorganic hybrid membranes for selective separation applications is developed. This approach combines co-assembly of block copolymer (BCP) and inorganic nanoparticles (NPs) with non-solvent induced phase separation. The method is successfully applied to two distinct molar mass BCPs with different fractions of titanium dioxide (TiO2) NPs. The resulting hybrid membranes exhibit structural asymmetry with a thin nanoporous surface layer on top of a macroporous fingerlike support layer. Key parameters that dictate membrane surface morphology include the fraction of inorganics used and the length of time allowed for surface layer development. The resulting membranes exhibit both good selectivity and high permeability (3200 ± 500 Lm(-2) h(-1) bar(-1)). This fast and straightforward synthesis method for asymmetric hybrid membranes provides a new self-assembly platform upon which multifunctional and high-performance organic-inorganic hybrid membranes can be formed.

Prediction of binary nanoparticle superlattices from soft potentials

DOE PAGES

Horst, Nathan; Travesset, Alex

2016-01-07

Driven by the hypothesis that a sufficiently continuous short-ranged potential is able to account for shell flexibility and phonon modes and therefore provides a more realistic description of nanoparticle interactions than a hard sphere model, we compute the solid phase diagram of particles of different radii interacting with an inverse power law potential. From a pool of 24 candidate lattices, the free energy is optimized with respect to additional internal parameters and the p-exponent, determining the short-range properties of the potential, is varied between p = 12 and p = 6. The phase diagrams contain the phases found in ongoingmore » self-assembly experiments, including DNA programmable self-assembly and nanoparticles with capping ligands assembled by evaporation from an organic solvent. Thus, the resulting phase diagrams can be mapped quantitatively to existing experiments as a function of only two parameters: Nanoparticle radius ratio (γ) and softness asymmetry.« less

A General Approach for Fluid Patterning and Application in Fabricating Microdevices.

PubMed

Huang, Zhandong; Yang, Qiang; Su, Meng; Li, Zheng; Hu, Xiaotian; Li, Yifan; Pan, Qi; Ren, Wanjie; Li, Fengyu; Song, Yanlin

2018-06-19

Engineering the fluid interface such as the gas-liquid interface is of great significance for solvent processing applications including functional material assembly, inkjet printing, and high-performance device fabrication. However, precisely controlling the fluid interface remains a great challenge owing to its flexibility and fluidity. Here, a general method to manipulate the fluid interface for fluid patterning using micropillars in the microchannel is reported. The principle of fluid patterning for immiscible fluid pairs including air, water, and oils is proposed. This understanding enables the preparation of programmable multiphase fluid patterns and assembly of multilayer functional materials to fabricate micro-optoelectronic devices. This general strategy of fluid patterning provides a promising platform to study the fundamental processes occurring on the fluid interface, and benefits applications in many subjects, such as microfluidics, microbiology, chemical analysis and detection, material synthesis and assembly, device fabrication, etc. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Supramolecular amplification of amyloid self-assembly by iodination

NASA Astrophysics Data System (ADS)

Bertolani, Arianna; Pirrie, Lisa; Stefan, Loic; Houbenov, Nikolay; Haataja, Johannes S.; Catalano, Luca; Terraneo, Giancarlo; Giancane, Gabriele; Valli, Ludovico; Milani, Roberto; Ikkala, Olli; Resnati, Giuseppe; Metrangolo, Pierangelo

2015-06-01

Amyloid supramolecular assemblies have found widespread exploitation as ordered nanomaterials in a range of applications from materials science to biotechnology. New strategies are, however, required for understanding and promoting mature fibril formation from simple monomer motifs through easy and scalable processes. Noncovalent interactions are key to forming and holding the amyloid structure together. On the other hand, the halogen bond has never been used purposefully to achieve control over amyloid self-assembly. Here we show that single atom replacement of hydrogen with iodine, a halogen-bond donor, in the human calcitonin-derived amyloidogenic fragment DFNKF results in a super-gelator peptide, which forms a strong and shape-persistent hydrogel at 30-fold lower concentration than the wild-type pentapeptide. This is remarkable for such a modest perturbation in structure. Iodination of aromatic amino acids may thus develop as a general strategy for the design of new hydrogels from unprotected peptides and without using organic solvents.

Charged triblock copolymer self-assembly into charged micelles

NASA Astrophysics Data System (ADS)

Chen, Yingchao; Zhang, Ke; Zhu, Jiahua; Wooley, Karen; Pochan, Darrin; Department of Material Science; Engineering University of Delaware Team; Department of Chemistry Texas A&M University Collaboration

2011-03-01

Micelles were formed through the self-assembly of amphiphlic block copolymer poly(acrylic acid)-block-poly(methyl acrylate)-block-polystyrene (PAA-PMA-PS). ~Importantly, the polymer is complexed with diamine molecules in pure THF solution prior to water titration solvent processing-a critical aspect in the control of final micelle geometry. The addition of diamine triggers acid-base complexation ~between the carboxylic acid PAA side chains and amines. ~Remarkably uniform spheres were found to form close-packed patterns when forced into dried films and thin, solvated films when an excess of amine was used in the polymer assembly process. Surface properties and structural features of these hexagonal-packed spherical micelles with charged corona have been explored by various characterization methods including Transmission Electron Microscopy (TEM), cryogenic TEM, z-potential analysis and Dynamic Light Scattering. The forming mechanism for this pattern and morphology changes against external stimulate such as salt will be discussed.

Prediction of Binary Nanoparticle Superlattices from Soft Potentials

NASA Astrophysics Data System (ADS)

Horst, Nathan; Travesset, Alex

Driven by the hypothesis that a sufficiently continuous short-ranged potential is able to account for shell flexibility and phonon modes and therefore provides a more realistic description of nanoparticle interactions than a hard sphere model, we compute the solid phase diagram of particles of different radii interacting with an inverse power law potential. We explore 24 candidate lattices where the p-exponent, determining the short-range properties of the potential, is varied between p=12 and p=6, and optimize the free energy with respect to additional internal parameters. The phase diagrams contain the phases found in ongoing self-assembly experiments, including DNA programmable self-assembly and nanoparticles with capping ligands assembled by evaporation from an organic solvent. The resulting phase diagrams can be mapped quantitatively to existing experiments as a function of only two parameters: nanoparticle radius ratio (γ) and softness asymmetry (SA). Supported by DOE under Contract Number DE-AC02-07CH11358.

Engineering the entropy-driven free-energy landscape of a dynamic nanoporous protein assembly.

PubMed

Alberstein, Robert; Suzuki, Yuta; Paesani, Francesco; Tezcan, F Akif

2018-04-30

De novo design and construction of stimuli-responsive protein assemblies that predictably switch between discrete conformational states remains an essential but highly challenging goal in biomolecular design. We previously reported synthetic, two-dimensional protein lattices self-assembled via disulfide bonding interactions, which endows them with a unique capacity to undergo coherent conformational changes without losing crystalline order. Here, we carried out all-atom molecular dynamics simulations to map the free-energy landscape of these lattices, validated this landscape through extensive structural characterization by electron microscopy and established that it is predominantly governed by solvent reorganization entropy. Subsequent redesign of the protein surface with conditionally repulsive electrostatic interactions enabled us to predictably perturb the free-energy landscape and obtain a new protein lattice whose conformational dynamics can be chemically and mechanically toggled between three different states with varying porosities and molecular densities.

Prediction of binary nanoparticle superlattices from soft potentials

NASA Astrophysics Data System (ADS)

Horst, Nathan; Travesset, Alex

2016-01-01

Driven by the hypothesis that a sufficiently continuous short-ranged potential is able to account for shell flexibility and phonon modes and therefore provides a more realistic description of nanoparticle interactions than a hard sphere model, we compute the solid phase diagram of particles of different radii interacting with an inverse power law potential. From a pool of 24 candidate lattices, the free energy is optimized with respect to additional internal parameters and the p-exponent, determining the short-range properties of the potential, is varied between p = 12 and p = 6. The phase diagrams contain the phases found in ongoing self-assembly experiments, including DNA programmable self-assembly and nanoparticles with capping ligands assembled by evaporation from an organic solvent. The resulting phase diagrams can be mapped quantitatively to existing experiments as a function of only two parameters: Nanoparticle radius ratio (γ) and softness asymmetry.

Exciplex mediated photoinduced electron transfer reactions of phthalocyanine-fullerene dyads.

PubMed

Niemi, Marja; Tkachenko, Nikolai V; Efimov, Alexander; Lehtivuori, Heli; Ohkubo, Kei; Fukuzumi, Shunichi; Lemmetyinen, Helge

2008-07-31

Evidences of an intramolecular exciplex intermediate in a photoinduced electron transfer (ET) reaction of double-linked free-base and zinc phthalocyanine-C60 dyads were found. This was the first time for a dyad with phthalocyanine donor. Excitation of the phthalocyanine moiety of the dyads results in rapid ET from phthalocyanine to fullerene via an exciplex state in both polar and nonpolar solvents. Relaxation of the charge-separated (CS) state Pc(*+)-C60(*-) in a polar solvent occurs directly to the ground state in 30-70 ps. In a nonpolar solvent, roughly 20% of the molecules undergo transition from the CS state to phthalocyanine triplet state (3)Pc*-C60 before relaxation to the ground state. Formation of the CS state was confirmed with electron spin resonance measurements at low temperature in both polar and nonpolar solvent. Reaction schemes for the photoinduced ET reactions of the dyads were completed with rate constants obtained from the time-resolved absorption and emission measurements and with state energies obtained from the fluorescence, phosphorescence, and voltammetric measurements.

Exploring Solvent Shape and Function Using - and Isomer-Selective Vibrational Spectroscopy

NASA Astrophysics Data System (ADS)

Johnson, Mark

2010-06-01

We illustrate the new types of information than can be obtained through isomer-selective ``hole-burning'' spectroscopy carried out in the vibrational manifolds of Ar-tagged cluster ions. Three examples of increasing complexity will be presented where the changes in a solute ion are correlated with different morphologies of a surrounding solvent cage. In the first, we discuss the weak coupling limit where different hydration morphologies lead to small distortions of a covalent ion. We then introduce the more interesting case of the hydrated electron, where different shapes of the water network lead to dramatic changes in the extent of delocalization in the diffuse excess electron cloud. We then turn to the most complex case involving hydration of the nitrosonium ion, where different arrangements of the same number of water molecules span the range in behavior from simple solvation to actively causing a chemical reaction. The latter results are particularly interesting as they provide a microscopic, molecular-level picture of the ``solvent coordinate'' commonly used to describe solvent mediated processes.

Enzymatic hybridization of α-lipoic acid with bioactive compounds in ionic solvents.

PubMed

Papadopoulou, Athena A; Katsoura, Maria H; Chatzikonstantinou, Alexandra; Kyriakou, Eleni; Polydera, Angeliki C; Tzakos, Andreas G; Stamatis, Haralambos

2013-05-01

The lipase-catalyzed molecular hybridization of α-lipoic acid (LA) with bioactive compounds pyridoxine, tyrosol and tyramine was performed in ionic solvents and deep eutectic solvents. The biocatalytic reactions were catalyzed by Candida antarctica lipase B immobilized onto various functionalized multi-walled carbon nanotubes (f-CNTs-CaLB), as well as by commercial Novozym 435. The use of f-CNTs-CaLB leads, in most cases, to higher conversion yields as compared to Novozym 435. The nature and ion composition of ionic solvents affect the performance of the biocatalytic process. The highest conversion yield was observed in (mtoa)NTf2. The high enzyme stability and the relatively low solubility of substrates in specific media account for the improved biocatalytic synthesis of molecular hybrids of LA. Principal component analysis was used to screen for potential lipoxygenase inhibitors. In vitro studies showed that the synthesized compounds exhibit up to 10-fold increased inhibitory activity on lipoxygenase mediated lipid peroxidation as compared to parent molecules. Copyright © 2013 Elsevier Ltd. All rights reserved.

Atomistic Simulations of Hydrodynamic and Interaction Forces on Functionalized Silica Nanoparticles

NASA Astrophysics Data System (ADS)

Lane, J. Matthew D.; Ismail, Ahmed E.; Chandross, Michael; Lorenz, Christian D.; Grest, Gary S.

2009-03-01

It is often desired to prevent the flocculation and phase separation of nanoparticles in solution. This can be accomplished either by manipulating the solvent or by tailoring the surface chemistry of the nanoparticles through functionalization with a monolayer of oligomer chains. Since it is not known how these functionalized coatings affect the interactions between nanoparticles and with the surrounding solvent, we present results from a series of molecular dynamics simulations of polyethylene oxide (PEO) coated silica nanoparticles of varying size (5 to 20 nm diameter) in water. For a single nanoparticle we determined the Stokes drag on the nanoparticle as it moves through the solvent and as it approaches a wall. Due to hydrodynamic interactions there are large finite size effects which we estimate by varying the size of the simulation cell. We also determined both solvent-mediated (velocity-independent) and lubrication (velocity-dependent) forces between two nanoparticles as a function of the coverage and chain length of the PEO chains.

Full color stop bands in hybrid organic/inorganic block copolymer photonic gels by swelling-freezing.

PubMed

Kang, Changjoon; Kim, Eunjoo; Baek, Heeyoel; Hwang, Kyosung; Kwak, Dongwoo; Kang, Youngjong; Thomas, Edwin L

2009-06-10

We report a facile way of fabricating hybrid organic/inorganic photonic gels by selective swelling and subsequent infiltration of SiO(2) into one type of lamellar microdomain previously self-assembled from modest-molecular-weight block copolymers. Transparent, in-plane lamellar films were first prepared by assembly of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP), and subsequently the P2VP domains were swollen with a selective solvent, methanol. The swollen structures were then fixated by synthesizing SiO(2) nanoparticles within P2VP domains. The resulting frozen photonic gels (f-photonic gels) exhibited strong reflective colors with stop bands across the visible region of wavelengths.

Soft nanoparticles: nano ionic networks of associated ionic polymers

DOE PAGES

Aryal, Dipak; Grest, Gary S.; Perahia, Dvora

2017-01-01

Directing the formation of nanostructures that serve as building blocks of membranes presents an immense step towards engineering controlled polymeric ion transport systems. Here, using the exquisite atomic detail captured by molecular dynamics simulations, we follow the assembly of a co-polymer that consists of polystyrene sulfonate tethered symmetrically to hydrophobic blocks, realizing a new type of long lived solvent-responsive soft nanoparticle.

Photoinitated charge separation in a hybrid titanium dioxide metalloporphyrin peptide material

NASA Astrophysics Data System (ADS)

Fry, H. Christopher; Liu, Yuzi; Dimitrijevic, Nada M.; Rajh, Tijana

2014-08-01

In natural systems, electron flow is mediated by proteins that spatially organize donor and acceptor molecules with great precision. Achieving this guided, directional flow of information is a desirable feature in photovoltaic media. Here, we design self-assembled peptide materials that organize multiple electronic components capable of performing photoinduced charge separation. Two peptides, c16-AHL3K3-CO2H and c16-AHL3K9-CO2H, self-assemble into fibres and provide a scaffold capable of binding a metalloporphyrin via histidine axial ligation and mineralize titanium dioxide (TiO2) on the lysine-rich surface of the resulting fibrous structures. Electron paramagnetic resonance studies of this self-assembled material under continuous light excitation demonstrate charge separation induced by excitation of the metalloporphyrin and mediated by the peptide assembly structure. This approach to dye-sensitized semiconducting materials offers a means to spatially control the dye molecule with respect to the semiconducting material through careful, strategic peptide design.

Pre-transition effects mediate forces of assembly between transmembrane proteins

DOE PAGES

Katira, Shachi; Mandadapu, Kranthi K.; Vaikuntanathan, Suriyanarayanan; ...

2016-02-24

We present a mechanism for a generic, powerful force of assembly and mobility for transmembrane proteins in lipid bilayers. This force is a pre-transition (or pre-melting) effect for the first-order transition between ordered and disordered phases in the membrane. Using large-scale molecular simulation, we show that a protein with hydrophobic thickness equal to that of the disordered phase embedded in an ordered bilayer stabilizes a microscopic order–disorder interface. The stiffness of that interface is finite. When two such proteins approach each other, they assemble because assembly reduces the net interfacial energy. Analogous to the hydrophobic effect, we refer to thismore » phenomenon as the 'orderphobic effect'. The effect is mediated by proximity to the order–disorder phase transition and the size and hydrophobic mismatch of the protein. The strength and range of forces arising from this effect are significantly larger than those that could arise from membrane elasticity for the membranes considered.« less

Pre-transition effects mediate forces of assembly between transmembrane proteins

PubMed Central

Katira, Shachi; Mandadapu, Kranthi K; Vaikuntanathan, Suriyanarayanan; Smit, Berend; Chandler, David

2016-01-01

We present a mechanism for a generic, powerful force of assembly and mobility for transmembrane proteins in lipid bilayers. This force is a pre-transition (or pre-melting) effect for the first-order transition between ordered and disordered phases in the membrane. Using large-scale molecular simulation, we show that a protein with hydrophobic thickness equal to that of the disordered phase embedded in an ordered bilayer stabilizes a microscopic order–disorder interface. The stiffness of that interface is finite. When two such proteins approach each other, they assemble because assembly reduces the net interfacial energy. Analogous to the hydrophobic effect, we refer to this phenomenon as the 'orderphobic effect'. The effect is mediated by proximity to the order–disorder phase transition and the size and hydrophobic mismatch of the protein. The strength and range of forces arising from this effect are significantly larger than those that could arise from membrane elasticity for the membranes considered. DOI: http://dx.doi.org/10.7554/eLife.13150.001 PMID:26910009

Fragile X mental retardation protein stimulates ribonucleoprotein assembly of influenza A virus

NASA Astrophysics Data System (ADS)

Zhou, Zhuo; Cao, Mengmeng; Guo, Yang; Zhao, Lili; Wang, Jingfeng; Jia, Xue; Li, Jianguo; Wang, Conghui; Gabriel, Gülsah; Xue, Qinghua; Yi, Yonghong; Cui, Sheng; Jin, Qi; Wang, Jianwei; Deng, Tao

2014-02-01

The ribonucleoprotein (RNP) of the influenza A virus is responsible for the transcription and replication of viral RNA in the nucleus. These processes require interplay between host factors and RNP components. Here, we report that the Fragile X mental retardation protein (FMRP) targets influenza virus RNA synthesis machinery and facilitates virus replication both in cell culture and in mice. We demonstrate that FMRP transiently associates with viral RNP and stimulates viral RNP assembly through RNA-mediated interaction with the nucleoprotein. Furthermore, the KH2 domain of FMRP mediates its association with the nucleoprotein. A point mutation (I304N) in the KH2 domain, identified from a Fragile X syndrome patient, disrupts the FMRP-nucleoprotein association and abolishes the ability of FMRP to participate in viral RNP assembly. We conclude that FMRP is a critical host factor used by influenza viruses to facilitate viral RNP assembly. Our observation reveals a mechanism of influenza virus RNA synthesis and provides insights into FMRP functions.

Fuel-Mediated Transient Clustering of Colloidal Building Blocks.

PubMed

van Ravensteijn, Bas G P; Hendriksen, Wouter E; Eelkema, Rienk; van Esch, Jan H; Kegel, Willem K

2017-07-26

Fuel-driven assembly operates under the continuous influx of energy and results in superstructures that exist out of equilibrium. Such dissipative processes provide a route toward structures and transient behavior unreachable by conventional equilibrium self-assembly. Although perfected in biological systems like microtubules, this class of assembly is only sparsely used in synthetic or colloidal analogues. Here, we present a novel colloidal system that shows transient clustering driven by a chemical fuel. Addition of fuel causes an increase in hydrophobicity of the building blocks by actively removing surface charges, thereby driving their aggregation. Depletion of fuel causes reappearance of the charged moieties and leads to disassembly of the formed clusters. This reassures that the system returns to its initial, equilibrium state. By taking advantage of the cyclic nature of our system, we show that clustering can be induced several times by simple injection of new fuel. The fuel-mediated assembly of colloidal building blocks presented here opens new avenues to the complex landscape of nonequilibrium colloidal structures, guided by biological design principles.

Pre-transition effects mediate forces of assembly between transmembrane proteins

DOE PAGES

Katira, Sachi; Mandadapu, Kranthi K.; Vaikuntanathan, Suriyanarayanan; ...

2016-02-24

We present a mechanism for a generic, powerful force of assembly and mobility for transmembrane proteins in lipid bilayers. This force is a pre-transition (or pre-melting) effect for the first-order transition between ordered and disordered phases in the membrane. Using large-scale molecular simulation, we show that a protein with hydrophobic thickness equal to that of the disordered phase embedded in an ordered bilayer stabilizes a microscopic order-disorder interface. The stiffness of that interface is finite. When two such proteins approach each other, they assemble because assembly reduces the net interfacial energy. Analogous to the hydrophobic effect, we refer to thismore » phenomenon as the ‘orderphobic effect’. The effect is mediated by proximity to the order-disorder phase transition and the size and hydrophobic mismatch of the protein. Furthermore, the strength and range of forces arising from this effect are significantly larger than those that could arise from membrane elasticity for the membranes considered.« less

Pre-transition effects mediate forces of assembly between transmembrane proteins

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katira, Shachi; Mandadapu, Kranthi K.; Vaikuntanathan, Suriyanarayanan

We present a mechanism for a generic, powerful force of assembly and mobility for transmembrane proteins in lipid bilayers. This force is a pre-transition (or pre-melting) effect for the first-order transition between ordered and disordered phases in the membrane. Using large-scale molecular simulation, we show that a protein with hydrophobic thickness equal to that of the disordered phase embedded in an ordered bilayer stabilizes a microscopic order–disorder interface. The stiffness of that interface is finite. When two such proteins approach each other, they assemble because assembly reduces the net interfacial energy. Analogous to the hydrophobic effect, we refer to thismore » phenomenon as the 'orderphobic effect'. The effect is mediated by proximity to the order–disorder phase transition and the size and hydrophobic mismatch of the protein. The strength and range of forces arising from this effect are significantly larger than those that could arise from membrane elasticity for the membranes considered.« less

Pre-transition effects mediate forces of assembly between transmembrane proteins

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katira, Sachi; Mandadapu, Kranthi K.; Vaikuntanathan, Suriyanarayanan

We present a mechanism for a generic, powerful force of assembly and mobility for transmembrane proteins in lipid bilayers. This force is a pre-transition (or pre-melting) effect for the first-order transition between ordered and disordered phases in the membrane. Using large-scale molecular simulation, we show that a protein with hydrophobic thickness equal to that of the disordered phase embedded in an ordered bilayer stabilizes a microscopic order-disorder interface. The stiffness of that interface is finite. When two such proteins approach each other, they assemble because assembly reduces the net interfacial energy. Analogous to the hydrophobic effect, we refer to thismore » phenomenon as the ‘orderphobic effect’. The effect is mediated by proximity to the order-disorder phase transition and the size and hydrophobic mismatch of the protein. Furthermore, the strength and range of forces arising from this effect are significantly larger than those that could arise from membrane elasticity for the membranes considered.« less

Cluster-mediated assembly enables step-growth copolymerization from binary nanoparticle mixtures with rationally designed architectures† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c8sc00220g

PubMed Central

Zhang, Xianfeng; Lv, Longfei; Wu, Guanhong; Yang, Dong

2018-01-01

Directed co-assembly of binary nanoparticles (NPs) into one-dimensional copolymer-like chains is fascinating but challenging in the realm of material science. While many strategies have been developed to induce the polymerization of NPs, it remains a grand challenge to produce colloidal copolymers with widely tailored compositions and precisely controlled architectures. Herein we report a robust colloidal polymerization strategy, which enables the growth of sophisticated NP chains with elaborately designed structures. By quantifying NP assembly statistics and kinetics, we establish that the linear assembly of colloidal NPs, with the assistance of PbSO4 clusters, follows a step-growth polymerization mechanism, and on the basis of this, we design and fabricate NP chains structurally analogous to random, block, and alternating copolymers, respectively. Our studies offer mechanistic insights into cluster-mediated colloidal polymerization, paving the way toward the rational synthesis of colloidal copolymers with quantitatively predicted architectures and functionalities. PMID:29862003

Novel Self-Assembling Amino Acid-Derived Block Copolymer with Changeable Polymer Backbone Structure.

PubMed

Koga, Tomoyuki; Aso, Eri; Higashi, Nobuyuki

2016-11-29

Block copolymers have attracted much attention as potentially interesting building blocks for the development of novel nanostructured materials in recent years. Herein, we report a new type of self-assembling block copolymer with changeable polymer backbone structure, poly(Fmoc-Ser) ester -b-PSt, which was synthesized by combining the polycondensation of 9-fluorenylmethoxycarbonyl-serine (Fmoc-Ser) with the reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene (St). This block copolymer showed the direct conversion of the backbone structure from polyester to polypeptide through a multi O,N-acyl migration triggered by base-induced deprotection of Fmoc groups in organic solvent. Such polymer-to-polymer conversion was found to occur quantitatively without decrease in degree of polymerization and to cause a drastic change in self-assembling property of the block copolymer. On the basis of several morphological analyses using FTIR spectroscopy, atomic force, and transmission and scanning electron microscopies, the resulting peptide block copolymer was found to self-assemble into a vesicle-like hollow nanosphere with relatively uniform diameter of ca. 300 nm in toluene. In this case, the peptide block generated from polyester formed β-sheet structure, indicating the self-assembly via peptide-guided route. We believe the findings presented in this study offer a new concept for the development of self-assembling block copolymer system.

Analysis of the complex formation, interaction and electron transfer pathway between the "open" conformation of NADPH-cytochrome P450 reductase and aromatase.

PubMed

Dai, Yuejie; Zhen, Jing; Zhang, Xiuli; Zhong, Yonghui; Liu, Shaodan; Sun, Ziyue; Guo, Yue; Wu, Qingli

2015-09-01

The complex structure of human aromatase (CYP19) and the open form of ΔTGEE mutant NADPH-cytochrome P450 reductase (mCPR) was constructed using template-based protein alignment method. Dynamic simulation of formed complex was performed on NAMD 2.9, in which CHARMm all 27_prot_lipid_na force field and an explicit TIP3P water solvent model were applied. The result showed mCPR in its open conformation could steadily combine with aromatase from the proximal face. Data analysis indicates hydrogen bonds and four salt bridges on the binding surface enhance the interaction between the two protein molecules. Amino acid, Lys108 plays a key role in aromatase activity through the formation of a salt bridge with Asp147 and two hydrogen bonds with Asp147 and Gln150 in mCPR. The optimal pathway for the first electron transfer from CPR to aromatase was revealed and calculated using HARLEM software. The rates for solvent mediated and non-solvent mediated electron transfer from FMNH2 to heme were determined as 1.04×10(6)s(-)(1) and 4.86×10(5)s(-)(1) respectively, which indicates the solvent water can facilitate the electron transfer from FMNH2 to heme. This study presents a novel strategy for the study of the protein-protein interactions based on the template-based protein alignment, which may help new aromtase development targeting the electron transfer between mCPR and aromatase. Copyright © 2015 Elsevier Inc. All rights reserved.

Human microcephaly protein RTTN interacts with STIL and is required to build full-length centrioles.

PubMed

Chen, Hsin-Yi; Wu, Chien-Ting; Tang, Chieh-Ju C; Lin, Yi-Nan; Wang, Won-Jing; Tang, Tang K

2017-08-15

Mutations in many centriolar protein-encoding genes cause primary microcephaly. Using super-resolution and electron microscopy, we find that the human microcephaly protein, RTTN, is recruited to the proximal end of the procentriole at early S phase, and is located at the inner luminal walls of centrioles. Further studies demonstrate that RTTN directly interacts with STIL and acts downstream of STIL-mediated centriole assembly. CRISPR/Cas9-mediated RTTN gene knockout in p53-deficient cells induce amplification of primitive procentriole bodies that lack the distal-half centriolar proteins, POC5 and POC1B. Additional analyses show that RTTN serves as an upstream effector of CEP295, which mediates the loading of POC1B and POC5 to the distal-half centrioles. Interestingly, the naturally occurring microcephaly-associated mutant, RTTN (A578P), shows a low affinity for STIL binding and blocks centriole assembly. These findings reveal that RTTN contributes to building full-length centrioles and illuminate the molecular mechanism through which the RTTN (A578P) mutation causes primary microcephaly.Mutations in many centriolar protein-encoding genes cause primary microcephaly. Here the authors show that human microcephaly protein RTTN directly interacts with STIL and acts downstream of STIL-mediated centriole assembly, contributing to building full-length centrioles.

A basic domain in the histone H2B N-terminal tail is important for nucleosome assembly by FACT

PubMed Central

Mao, Peng; Kyriss, McKenna N. M.; Hodges, Amelia J.; Duan, Mingrui; Morris, Robert T.; Lavine, Mark D.; Topping, Traci B.; Gloss, Lisa M.; Wyrick, John J.

2016-01-01

Nucleosome assembly in vivo requires assembly factors, such as histone chaperones, to bind to histones and mediate their deposition onto DNA. In yeast, the essential histone chaperone FACT (FAcilitates Chromatin Transcription) functions in nucleosome assembly and H2A–H2B deposition during transcription elongation and DNA replication. Recent studies have identified candidate histone residues that mediate FACT binding to histones, but it is not known which histone residues are important for FACT to deposit histones onto DNA during nucleosome assembly. In this study, we report that the histone H2B repression (HBR) domain within the H2B N-terminal tail is important for histone deposition by FACT. Deletion of the HBR domain causes significant defects in histone occupancy in the yeast genome, particularly at HBR-repressed genes, and a pronounced increase in H2A–H2B dimers that remain bound to FACT in vivo. Moreover, the HBR domain is required for purified FACT to efficiently assemble recombinant nucleosomes in vitro. We propose that the interaction between the highly basic HBR domain and DNA plays an important role in stabilizing the nascent nucleosome during the process of histone H2A–H2B deposition by FACT. PMID:27369377

Highly selective and sensitive method for Cu2+ detection based on chiroptical activity of L-Cysteine mediated Au nanorod assemblies.

PubMed

Abbasi, Shahryar; Khani, Hamzeh

2017-11-05

Herein, we demonstrated a simple and efficient method to detect Cu 2+ based on amplified optical activity in the chiral nanoassemblies of gold nanorods (Au NRs). L-Cysteine can induce side-by-side or end-to-end assembly of Au NRs with an evident plasmonic circular dichroism (PCD) response due to coupling between surface plasmon resonances (SPR) of Au NRs and the chiral signal of L-Cys. Because of the obvious stronger plasmonic circular dichrosim (CD) response of the side-by-side assembly compared with the end-to-end assemblies, SS assembled Au NRs was selected as a sensitive platform and used for Cu 2+ detection. In the presence of Cu 2+ , Cu 2+ can catalyze O 2 oxidation of cysteine to cystine. With an increase in Cu 2+ concentration, the L-Cysteine-mediated assembly of Au NRs decreased because of decrease in the free cysteine thiol groups, and the PCD signal decreased. Taking advantage of this method, Cu 2+ could be detected in the concentration range of 20pM-5nM. Under optimal conditions, the calculated detection limit was found to be 7pM. Copyright © 2017 Elsevier B.V. All rights reserved.

Multiscale and Multifunctional Emulsions by Host–Guest Interaction-Mediated Self-Assembly

PubMed Central

2018-01-01

Emulsions are widely used in numerous fields. Therefore, there has been increasing interest in the development of new emulsification strategies toward emulsions with advanced functions. Herein we report the formation of diverse emulsions by host–guest interaction-mediated interfacial self-assembly under mild conditions. In this strategy, a hydrophilic diblock copolymer with one block containing β-cyclodextrin (β-CD) can assemble at the oil/water interface when its aqueous solution is mixed with an oil phase of benzyl alcohol (BA), by host–guest interactions between β-CD and BA. This results in significantly reduced interfacial tension and the formation of switchable emulsions with easily tunable droplet sizes. Furthermore, nanoemulsions with excellent stability are successfully prepared simply via vortexing. The self-assembled oil-in-water emulsions also show catastrophic phase inversion, which can generate stable bicontinuous phase and water-in-oil emulsions, thereby further extending phase structures that can be realized by this host–guest self-assembly approach. Moreover, the host–guest nanoemulsions are able to engineer different nanoparticles and microstructures as well as solubilize a diverse array of hydrophobic drugs and dramatically enhance their oral bioavailability. The host–guest self-assembly emulsification is facile, energetically friendly, and fully translatable to industry, therefore representing a conceptually creative approach toward advanced emulsions. PMID:29806006

Single-layer graphene-assembled 3D porous carbon composites with PVA and Fe₃O₄ nano-fillers: an interface-mediated superior dielectric and EMI shielding performance.

PubMed

Rao, B V Bhaskara; Yadav, Prasad; Aepuru, Radhamanohar; Panda, H S; Ogale, Satishchandra; Kale, S N

2015-07-28

In this study, a novel composite of Fe3O4 nanofiller-decorated single-layer graphene-assembled porous carbon (SLGAPC) with polyvinyl alcohol (PVA) having flexibility and a density of 0.75 g cm(-3) is explored for its dielectric and electromagnetic interference (EMI) response properties. The composite is prepared by the solution casting method and its constituents are optimized as 15 wt% SLGAPC and 20 wt% Fe3O4 through a novel solvent relaxation nuclear magnetic resonance experiment. The PVA-SLGAPC-Fe3O4 composite shows high dielectric permittivity in the range of 1 Hz-10 MHz, enhanced by a factor of 4 as compared to that of the PVA-SLGAPC composite, with a reduced loss by a factor of 2. The temperature dependent dielectric properties reveal the activation energy behaviour with reference to the glass transition temperature (80 °C) of PVA. The dielectric hysteresis with the temperature cycle reveals a remnant polarization. The enhanced dielectric properties are suggested to be the result of improvement in the localized polarization of the integrated interface system (Maxwell-Wagner-Sillars (MWS) polarization) formed by the uniform adsorption of Fe3O4 on the surface of SLGAPC conjugated with PVA. The EMI shielding property of the composite with a low thickness of 0.3 mm in the X-band (8.2-12.4 GHz) shows a very impressive shielding efficiency of ∼15 dB and a specific shielding effectiveness of 20 dB (g cm(-3))(-1), indicating the promising character of this material for flexible EMI shielding applications.

Case-control study of leatherwork and male infertility

PubMed Central

Kurinczuk, J; Clarke, M

2001-01-01

OBJECTIVES—To test the hypothesis that leatherwork is associated with male infertility mediated through the development of oligozoospermia. The basis of any association was postulated, at the outset, to be with exposure to the solvents used in leatherwork.
METHODS—All new referrals with infertility presenting in Leicestershire hospital clinics between November 1988 and September 1992 and Kettering District General Hospital from August 1990 were eligible to participate; 88.5% agreed to be interviewed. Exposure to leatherwork and work with solvents was defined by job title. Comparisons were made with fertile controls and in an analysis within men from infertile couples with oligozoospermia as the primary outcome. Effects on sperm motility and deformity were investigated secondarily. Analyses used logistic regression for binary outcomes and multilevel modelling for continuous outcomes.
RESULTS—1906 men were interviewed. Compared with the fertile controls the men from infertile couples were 1.10 times (95% confidence interval (95% CI) 0.46 to 2.63; p=0.99) more likely to be leatherworkers and 1.73 times (95% CI 1.26 to 2.38; p<0.001) more likely to work with solvents. Compared with other men, leatherworkers were 1.20 times (95% CI 0.43 to 3.33; p=0.73) more likely to present with oligozoospermia and 1.65 times (95% CI 0.37 to 7.30; p=0.51) more likely to present with teratozoospermia. Being a leatherworker was associated with only a 6% reduction in sperm concentration; motility and deformity were similarly unaffected by this exposure. Work with solvents did not statistically, nor clinically, increase the risk of oligozoospermia, teratozoospermia, or asthenozoospermia.
CONCLUSIONS—There was little evidence to support the hypothesis that leatherwork is associated with an increased risk of presenting with infertility or oligozoospermia. There was limited evidence that leatherwork is a risk factor for teratozoospermia. Workers with solvents were at an increased risk of presenting with infertility, although this was not mediated through effects on standard measures of semen quality; this finding merits further investigation.


Keywords: leatherwork; solvents; male infertility PMID:11245737

Oxidative stress-mediated hemolytic activity of solvent exchange-prepared fullerene (C60) nanoparticles

NASA Astrophysics Data System (ADS)

Trpkovic, Andreja; Todorovic-Markovic, Biljana; Kleut, Duska; Misirkic, Maja; Janjetovic, Kristina; Vucicevic, Ljubica; Pantovic, Aleksandar; Jovanovic, Svetlana; Dramicanin, Miroslav; Markovic, Zoran; Trajkovic, Vladimir

2010-09-01

The present study investigated the hemolytic properties of fullerene (C60) nanoparticles prepared by solvent exchange using tetrahydrofuran (nC60THF), or by mechanochemically assisted complexation with macrocyclic oligosaccharide gamma-cyclodextrin (nC60CDX) or the copolymer ethylene vinyl acetate-ethylene vinyl versatate (nC60EVA-EVV). The spectrophotometrical analysis of hemoglobin release revealed that only nC60THF, but not nC60CDX or nC60EVA-EVV, was able to cause lysis of human erythrocytes in a dose- and time-dependent manner. Atomic force microscopy revealed that nC60THF-mediated hemolysis was preceded by erythrocyte shrinkage and increase in cell surface roughness. A flow cytometric analysis confirmed a decrease in erythrocyte size and demonstrated a significant increase in reactive oxygen species production in red blood cells exposed to nC60THF. The nC60THF-triggered hemolytic activity was efficiently reduced by the antioxidants N-acetylcysteine and butylated hydroxyanisole, as well as by serum albumin, the most abundant protein in human blood plasma. These data indicate that nC60THF can cause serum albumin-preventable hemolysis through oxidative stress-mediated damage of the erythrocyte membrane.

The PHOTOSYNTHESIS AFFECTED MUTANT68–LIKE Protein Evolved from a PSII Assembly Factor to Mediate Assembly of the Chloroplast NAD(P)H Dehydrogenase Complex in Arabidopsis[W

PubMed Central

Armbruster, Ute; Rühle, Thilo; Kreller, Renate; Strotbek, Christoph; Zühlke, Jessica; Tadini, Luca; Blunder, Thomas; Hertle, Alexander P.; Qi, Yafei; Rengstl, Birgit; Nickelsen, Jörg; Frank, Wolfgang; Leister, Dario

2013-01-01

In vascular plants, the chloroplast NAD(P)H dehydrogenase complex (NDH-C) is assembled from five distinct subcomplexes, the membrane-spanning (subM) and the luminal (subL) subcomplexes, as well as subA, subB, and subE. The assembly process itself is poorly understood. Vascular plant genomes code for two related intrinsic thylakoid proteins, PHOTOSYNTHESIS-AFFECTED MUTANT68 (PAM68), a photosystem II assembly factor, and PHOTOSYNTHESIS-AFFECTED MUTANT68-LIKE (PAM68L). As we show here, inactivation of Arabidopsis thaliana PAM68L in the pam68l-1 mutant identifies PAM68L as an NDH-C assembly factor. The mutant lacks functional NDH holocomplexes and accumulates three distinct NDH-C assembly intermediates (subB, subM, and subA+L), which are also found in mutants defective in subB assembly (ndf5) or subM expression (CHLORORESPIRATORY REDUCTION4-3 mutant). NDH-C assembly in the cyanobacterium Synechocystis sp PCC 6803 and the moss Physcomitrella patens does not require PAM68 proteins, as demonstrated by the analysis of knockout lines for the single-copy PAM68 genes in these species. We conclude that PAM68L mediates the attachment of subB- and subM-containing intermediates to a complex that contains subA and subL. The evolutionary appearance of subL and PAM68L during the transition from mosses like P. patens to flowering plants suggests that the associated increase in the complexity of the NDH-C might have been facilitated by the recruitment of evolutionarily novel assembly factors like PAM68L. PMID:24096342

Solvent-dependent activation of intermediate excited states in the energy relaxation pathways of spheroidene.

PubMed

Maiuri, Margherita; Polli, Dario; Brida, Daniele; Lüer, Larry; LaFountain, Amy M; Fuciman, Marcel; Cogdell, Richard J; Frank, Harry A; Cerullo, Giulio

2012-05-14

In carotenoids internal conversion between the allowed (S(2)) and forbidden (S(1)) excited states occurs on a sub-picosecond timescale; the involvement of an intermediate excited state(s) (S(x)) mediating the process is controversial. Here we use high time resolution (sub-20 fs) broadband (1.2-2.5 eV) pump-probe spectroscopy to study the solvent dependence of excited state dynamics of spheroidene, a naturally-occurring carotenoid with ten conjugated double bonds. In the high polarizability solvent, CS(2), we find no evidence of an intermediate state, and the traditional three-level (S(0), S(1), S(2)) model fully accounts for the S(2)→ S(1) process. On the other hand, in the low polarizability solvent, cyclohexane, we find that rapid (~30 fs) relaxation to an intermediate state, S(x), lying between S(1) and S(2) is required to account for the data. We interpret these results as due to a shift of the S(2) energy, which positions the state above or below the energy of S(x) in response to changes in solvent polarizability. This journal is © the Owner Societies 2012

Simple method for assembly of CRISPR synergistic activation mediator gRNA expression array.

PubMed

Vad-Nielsen, Johan; Nielsen, Anders Lade; Luo, Yonglun

2018-05-20

When studying complex interconnected regulatory networks, effective methods for simultaneously manipulating multiple genes expression are paramount. Previously, we have developed a simple method for generation of an all-in-one CRISPR gRNA expression array. We here present a Golden Gate Assembly-based system of synergistic activation mediator (SAM) compatible CRISPR/dCas9 gRNA expression array for the simultaneous activation of multiple genes. Using this system, we demonstrated the simultaneous activation of the transcription factors, TWIST, SNAIL, SLUG, and ZEB1 a human breast cancer cell line. Copyright © 2018 Elsevier B.V. All rights reserved.