Rod Segments Research Articles

Self-organization of amphiphilic diblock rod-coil molecule into supramolecular honeycomb and cylindrical aggregates and its application as Suzuki coupling reaction

An aromatic amphiphilic molecule consisting of three biphenyl groups and one styrene unit linked together with ether bonds as a rigid rod segment, and poly(ethylene oxide) with 17 repeating units as a coil segment was synthesized and its self-assembly behavior in the bulk state and aqueous solution was examined by DSC, X-ray scattering, DLS and TEM. This molecule based on a rod building block self-assembles into lamellar or hexagonal perforated layer (HPL) structures in the crystalline phase or liquid crystalline mesophase. In an aqueous medium, the molecule self-assembles into cylindrical aggregates and can be used as a supramolecular reactor for the Suzuki coupling reaction.

Synergistic Effects on Second Harmonic Generation of Hybrid CdSe−Au Nanoparticles

Hybrid semiconductor-metal nanoparticles exhibit a combination of properties from the disparate components or even, more interestingly, synergetic properties which arise from the coupling between the two materials. In this work, we study the second harmonic generation (SHG) in CdSe-Au hybrid nanoparticles in comparison with their components, using the Hyper-Rayleigh scattering (HRS) method. Possible contribution of symmetry effects was studied by comparing symmetric two-sided gold-tipped CdSe nanodumbbells with asymmetric one-sided quantum dot-Au (QD-Au) hybrids. A simplistic view of a symmetry effect is disproved in this case by the experimental data, which shows an unexpected reduction in the SHG response in both cases, compared to the respective mixtures of Au and CdSe nanoparticles. For CdSe-Au hybrids with a long semiconductor rod segment, we find that the SHG response corresponds to a sum of the contributions from the semiconductor and the metal components. However, for QD-Au and smaller dumbbells, the SHG response is smaller than expected from a simple sum of the contribution from both components. This reduction is assigned to the effects related to the CdSe-Au interfacial region within these hybrids. A first plausible contribution to the reduction is the dephasing induced by the gold, leading to diminished SHG from the CdSe component. This reduced response of the semiconductor component is accompanied by reduced SHG from the gold component which is assigned to a partial change of the surface of the gold once an interface with CdSe is formed. These observations regarding the SHG response manifest the unique properties that arise from the combination of a semiconductor and a metal within one hybrid nanoparticle.

Mesoscale Surface Patterning of a Laterally‐Grafted Rod Amphiphile: Rings And Fibers

An aromatic amphiphilic molecule based on branched oligo(ethylene oxide) was synthesized. Evaporation-driven ring formation and Langmuir-Blodgett films are investigated by utilizing this rigid-flexible block molecule. The size of the rings is strongly dependent on the solvent evaporation rate and the concentration of the molecule. In case of fast evaporation, volcano-like rings are formed by evaporating solution of high concentration. Perfectly symmetrical rings with diameters in the range of 2-6 microm are obtained by evaporating solution of low concentration. The formation mechanism of the ring is briefly discussed. The molecule at the air-water interface exhibits excellent amphiphilic properties. Upon transferring the monolayer onto solid substrates, AFM revealed the formation of fine and long, straight fibers. By combining the data obtained from the isotherms, AFM, water contact angle measurements, and UV/Vis and fluorescence spectra, the fibers are suggested to be formed by pi-pi stacking interaction of the aromatic rod segments as the oligo(ethylene oxide) branches are submerged in the water subphase upon compression. The fiber formation is associated with the transformation of the aromatic rod segments from the face-on conformation to the edge-on conformation.

β-Cyclodextrin-Capped Polyrotaxanes: One-Pot Facile Synthesis via Click Chemistry and Use as Templates for Platinum Nanowires

Polyrotaxanes (PRs), in which α-cyclodextrins (α-CDs) were threaded onto poly(ethylene glycol) (PEG) chains capped with β-cyclodextrins (β-CDs), were prepared by click chemistry via a one-pot strategy in water at room temperature with high yield, up to 320 mg/100 mg PEG axis. The terminal β-CD cavity could be recognized by phenolphthalein and utilized to form a supramolecular block copolymer with alternate rod and coil segments via the formation of a host−guest inclusion complex with diadamantyl-terminated PEG. The prepared PR could further work as a novel template for the in situ deposition of platinum (Pt) nanoparticles (NPs) to fabricate metallic nanowires. TEM and SEM observations showed that the resulting polycrystalline nanowires with length of 50−200 nm and diameter of ca. 12 nm were composed of close-packed uniform Pt NPs with diameter of ca. 2.5 nm. The catalytic activity of the Pt nanowires was demonstrated by the reduction of 4-nitrophenol. The fascinating β-CD-capped PR is promising in a wide ...

Synthesis and self‐assembly of rod‐coil molecules with n‐shaped rod building block

AbstractThe rod‐coil molecules with n‐shaped rod building block, consisting of an anthracene unit and two biphenyl groups linked together with acetylenyl bonds at the 1,8‐position of anthracene as a rigid rod segment, and the alkyl or alkyloxy chains with various length (i.e., methoxy‐ (1), octyl‐ (2), hexadecyl‐ (3)) at the 10‐position of anthracene and poly(ethylene oxide) with the number of repeating units of 7 connected with biphenyl as coil segments were synthesized. The molecular structures were characterized by 1H NMR and MALDI‐TOF mass spectroscopy. The self‐assembling behavior of new type of molecules 1–3 was investigated by means of DSC, POM, and SAXS at the bulk state. These molecules with a n‐shaped rod building block segment self‐assemble into supramolecular structures through the combination of π–π stacking of rigid rod building blocks and microphase separation of the rod and coil blocks. SAXS studies reveal that molecules 1 and 2 show hexagonal columnar and rectangular columnar structures in the liquid crystalline phase, respectively; meanwhile, molecules 1–3 self‐organize into lamellar structures in the crystalline state. In addition, self‐assembling studies of molecules 1–3 by DLS and TEM indicated that these molecules self‐assemble into elongated nanofibers in aqueous medium. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1415–1422, 2010

Synthesis and self-assembly of coil–rod–coil molecules with lateral methyl and ethyl groups in the center of the rod segment

Rod–coil molecules, consisting of a flexible and a rigid block, have a strong capacity to self-assemble into a variety of ordered nanostructures in the bulk state. In this paper, we report the synthesis and characterization of the self-assembly behavior of coil–rod–coil oligomers. These new materials consist of five biphenyls linked together with ether bonds as a rod segment and incorporate lateral methyl or ethyl groups in the center of the rod building block and poly(ethylene oxide) (PEO) with a degree of polymerization (DP) of 7, 12 and 17 coil segments. Structural investigation of these molecules by means of differential scanning calorimetry (DSC) and X-ray scattering (XRD) in the bulk state reveals that side chains, methyl and ethyl groups in the middle of the rod segment, dramatically influence the self assembly behavior in the liquid-crystalline phase. Molecules containing a lateral methyl group based on PEO coil chain (DP of 12 and 17) self-organize into a hexagonally perforated layer (HPL) structure in the liquid- crystalline phase, while the molecule with a lateral ethyl group based on PEO coil chain (DP of 7) self-assembles into a 2-D rectangular columnar liquid-crystal structure. On further increasing of the coil length of the molecule containing ethyl group, the molecules self-organize into a 1-D lamellar structure in the crystalline phase.

Purification and Partial Characterization of a Lutein-Binding Protein from Human Retina

Dietary intake of lutein and zeaxanthin appears to be advantageous for protecting human retinal and macular tissues from degenerative disorders such as age-related macular degeneration. Selective concentration of just two of the many dietary carotenoids suggests that uptake and transport of these xanthophyll carotenoids into the human foveal region are mediated by specific xanthophyll-binding proteins such as GSTP1 which has previously been identified as the zeaxanthin-binding protein of the primate macula. Here, a membrane-associated human retinal lutein-binding protein (HR-LBP) was purified from human peripheral retina using ion-exchange chromatography followed by size-exclusion chromatography. After attaining 83-fold enrichment of HR-LBP, this protein exhibited a significant bathochromic shift of approximately 90 nm in association with lutein, and equilibrium binding studies demonstrated saturable, specific binding toward lutein with a K(D) of 0.45 muM. Examination for cross-reactivity with antibodies raised against known lutein-binding proteins from other organisms revealed consistent labeling of a major protein band of purified HR-LBP at approximately 29 kDa with an antibody raised against silkworm (Bombyx mori) carotenoid-binding protein (CBP), a member of steroidogenic acute regulatory (StAR) protein family with significant homology to many human StAR proteins. Immunolocalization with antibodies directed against either CBP or GSTP1 showed specific labeling of rod and cone inner segments, especially in the mitochondria-rich ellipsoid region. There was also strong labeling of the outer plexiform (Henle fiber) layer with anti-GSTP1. Such localizations compare favorably with the distribution of macular carotenoids as revealed by resonance Raman microscopy. Our results suggest that HR-LBP may facilitate lutein's localization to a region of the cell subject to considerable oxidative stress.

Synthesis and Self-Assembly of Coil−Rod Double Hydrophilic Diblock Copolymer with Dually Responsive Asymmetric Centipede-Shaped Polymer Brush as the Rod Segment

We report on the synthesis and self-assembly of well-defined coil−rod double hydrophilic diblock copolymer with pH- and thermo-responsive asymmetric centipede-shaped polymer brush as the rod segment via a combination of atom transfer radical polymerization (ATRP) and click chemistry (Schemes 1 and 2). At first, poly(ethylene oxide)-b-poly(glycidyl methacrylate), PEO-b-PGMA, was prepared by ATRP using PEO-based macroinitiator. The ring-opening of pendent epoxide moieties in PEO-b-PGMA with NaN3 followed by esterification with 2-bromoisobutyryl bromide afforded multifunctional PEO-b-[PGMA-(N3)(Br)] bearing one azide and one bromine moieties on each monomer repeating unit of PGMA. The subsequent ATRP of 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) using PEO-b-[PGMA-(N3)(Br)] as the macroinitiator yielded PEO-b-[PGMA-g-(N3)(PMEO2MA)] coil−brush diblock copolymer possessing one residual azide moiety at each grafting site. Finally, the target coil−rod diblock copolymer with asymmetric centipede-shaped polymer...

Chiral Assembly from Achiral Rod−Coil Molecules Triggered by Compression at the Air−Water Interface

A series of achiral rod-coil molecules consisting of an oligo(p-phenylene) conjugated rod with a poly(ethylene oxide) or poly(propylene oxide) coil laterally attached through an imidazole linkage were synthesized, and their interfacial behaviors were investigated. Compounds 1a and 1b have a similar surface behavior with a shoulder indicating a transformation of rod segments from flat-on to vertical orientation. Interestingly, CD and AFM suggest chiral films are formed when the LB films were deposited after the shoulder. Although compound 1c shows different surface behavior because the PEO chains dissolved into water upon compression, macroscopic chirality was also detected. In contrast, compound 2, based on a reduced conformational rigidity of the aromatic rod segment, does not form chiral assemblies. Combining the data collected, the cooperative interaction of the hydrogen bond between the molecules and pi-pi stacking as well as the steric constraint between the aromatic rod segments are responsible for the macroscopic chirality. Such kind of stacking can be realized through a molecular design and a lateral compression. A deep insight into the relationship between the molecular structure and the chirality was gained.

Cover Picture: Solid‐State Scrolls from Hierarchical Self‐Assembly of T‐Shaped Rod–Coil Molecules (Angew. Chem. Int. Ed. 9/2009)

AbstractSolid scrolls are reversibly formed by self‐assembly of rod‐shaped molecules with laterally attached coil units, in contrast to the layered structures formed from self‐assembly of planar molecules. As described by M. Lee and co‐workers in their Communication on page 1664 ff., the core structure of the scrolls, which are either filled cylinders or hollow tubes, can be controlled by variation of the length of the coil unit. The cover picture shows aligned tubular scrolls displaying well‐defined in‐plane ordering of the rod segments.magnified image

Plasmonic Focusing in Rod−Sheath Heteronanostructures

This paper describes the fabrication of plasmonic focusing, free-standing rod-sheath hetero-nanostructures based on electrochemical templated synthesis and selective chemical etching. These hetero-nanostructures take advantage of plasmon interference together with field enhancements due to sharp junction structures to function as stand-alone SERS substrates containing Raman hot spots at the interface of the rod and sheath segments. This result is investigated with empirical and theoretical (discrete dipole approximation, DDA) methods, and we show how plasmon interference can be tuned by varying the sheath and rod lengths.

Highly Luminescent BODIPY-Based Organoboron Polymer Exhibiting Supramolecular Self-Assemble Structure

A novel class of rod-coil type-organoboron polymers with p-phenylene-ethynylene as the rod segment and long alkyl chain (decyl group) as coil segment has been prepared from a Sonogashira-Hagihara coupling reaction of a BODIPY-based monomer having bis-iodophenyl and decyl groups with diyne monomers, 1,4-diethynylbenzene (a), 1,4-diethynyl-2,5-bis(trifluoromethyl)benzene (b), and 2,7-diethynyl-9,9-dihexyl-9H-fluorene (c). The characterization by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the strong tendency of the obtained polymers, 2a, 2b, and 2c, to self-assemble into particles in solution and as-casted films on a micron-nm scale. Especially, 2a showed the presence of nm-sized particles and micron-sized fiber-like structures formed by aggregation of each particle. Further, in CHCl3, the gelation of 2a by three-dimensional aggregation of each fiber was observed at room temperature after 24 h. Their luminescent properties showed high energy transfer efficiency from pi-conjugated polymer linkers to BODIPY moieties (PhiF > 71%).

Synthesis, characterization, and self‐assembly of ion‐bonded A2B rod‐coil copolymer with oligo(para‐phenyleneethynylene) as rod segment

AbstractSupramolecular A2B rod‐coil copolymer, composed of two polystyrene (PSt) arms and one oligo(para‐phenyleneethynylene) (OPE) arm linked via ionic bond, has been designed and successfully synthesized. First, a trifunctional initiator, methyl 1,3‐bis(bromomethyl)benzonate, was prepared and used to initiate the polymerization of styrene under atom transfer radical polymerization (ATRP) condition to provide polystyrene (PSt) carrying monoester group at the middle of polymer chain. Then, the ester group was transferred into tertiary amino group to give amino‐functionalized PSt, (PSt)2N(CH3)2. Subsequently, the ion‐bonded rod‐coil copolymer, (PSt)2OPE, was obtained by the reaction of (PSt)2N(CH3)2 with carboxy‐terminated OPE (OPECOOH). The resulting copolymer was characterized by nuclear magnetic resonance (NMR), Fourier transformer infrared (FTIR), and gel permeation chromatography (GPC) techniques. Vesicles and spherical micelles were generated from this supramolecular rod‐coil copolymer through the manipulation of the initial polymer concentration in toluene. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7667–7676, 2008

Bacterial flagella are firmly anchored.

There are mutants of Salmonella enterica (with mutations in fliF and fliL) that shed flagella when they are swimming in a viscous medium or on the surface of soft agar. Filaments with hooks and the distal rod segment FlgG are recovered. We tried to extract flagellar filaments from such cells by pulling on them with an optical trap but failed, even when we used forces large enough to straighten the filaments. Thus, flagella are firmly anchored.

Stepped Strips from Self-Organization of Oligo(p-phenylene) Rods with Lateral Dendritic Chains

We have demonstrated that the rod segments with lateral dendritic chains self-assemble into unique stepped strips in which the rods are aligned parallel to the strip long axis. This unique organization of the rod segments arises from a balance between the energetic gain of a parallel arrangement of the rods and the resulting entropic penalty associated with stretching of the lateral flexible chains.

Molecular Self-Assembly into One-Dimensional Nanostructures

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

Influence of pH on linear viscoelasticity and droplet size distribution of highly concentrated O/W crayfish flour-based emulsions

In the present work, the influence of pH on stability of oil-in-water (O/W; 75 wt%/25 wt%) emulsions stabilized by crayfish flour (CF) has been studied. CF (containing ca. 65 wt%) showed poor functionality in a wade range of pH, which inhibits formation of stable emulsions. An indirect procedure has been developed in order to obtain emulsion at a broad pH range, including isoelectric point (p I) value. The emulsions have been characterized by means of linear dynamic viscoelasticity and droplet size distribution (DSD) analysis. These emulsions present a behaviour characteristic of highly concentrated emulsions with a well-developed plateau region. The most unfavourable DSD and linear viscoelastic results correspond to the p I. A significant improvement takes place as the pH value departs from the p I. An exception for linear viscoelasticity results have been found at pH 10, which is close to the pI for rod segments of myofibrillar proteins. Stability of these emulsions has been studied by following the evolution of DSD and linear viscoelastic parameters along time. The poorer results in emulsion stability correspond to pH values close to the p I, at which the increase in droplet size or uniformity parameter as well as the decrease in the plateau modulus become more pronounced. Conversely, the stability significantly improves as the pH departs from p I.

The tektin family of microtubule-stabilizing proteins

Tektins are insoluble a-helical proteins essential for the construction of cilia and flagella and are found throughout the eukaryotes apart from higher plants.

A Model for Self-Assembly in Side Chain Liquid Crystalline Block Copolymers

We present a new model based on self-consistent field theory (SCFT) approach and complement it by strong segregation theory (SST) based calculations to characterize the self-assembly behavior in side-chain liquid crystalline block copolymers. Our model considers a micromechanical representation of flexible coil−coil diblock copolymers, with rodlike units grafted to one of the blocks. We present results which elucidate self-assembly arising from the interplay between block copolymer microphase separation and the orientational ordering of the rod segments. We determine the morphological phase diagram for this system by assuming two dimensional variations of composition profiles. Our numerical results are in very good agreement with reported experimental observations. Many of the traditional flexible diblock copolymer microphases are also predicted to occur for side chain liquid crystalline polymers, with smectic ordering accompanying within the microphases. The equilibrium phase morphologies are observed to depend on the molecular weight of the copolymer, the length of the rod units, the relative volume fractions of each block, and the energetic and orientational interactions between different components. Moreover, for the parameters considered in this article, microphase separation was observed to be a requisite for developing orientational ordering between mesogenic units. The results of SST provide a physical explanation for the observations and are in good agreement with that of the SCFT calculations.

Tunable Columnar Organization by Twisted Stacking of End-Capped Aromatic Rods

The dumbbell-shaped aromatic amphiphilic molecules consisting of hexa-p-phenylene-conjugated carbazole moieties on both ends as a rigid rod segment and oligoether chains with different cross-sectio...