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At least 127 records · Page 7Linked to original sources
PubMed2001

Modulating artificial membrane morphology: pH-induced chromatic transition and nanostructural transformation of a bolaamphiphilic conjugated polymer from blue helical ribbons to red nanofibers.

Design and characterization of helical ribbon assemblies of a bolaamphiphilic conjugated polymer and their color-coded transformation into nanofibers are described. An L-glutamic acid modified bolaamphiphilic diacetylene lipid was synthesized and self-assembled into right-handed helical ribbons with micron scale length and nano scale thickness under mild conditions. The ribbon structures were further stabilized by polymerizing well-aligned diacetylene units to form bisfunctional polydiacetylenes (PDAs). Transitions from flat sheets to helical ribbons and tubes were observed by transmission electron microscopy. The helical ribbons appear to originate from the rupture of flat sheets along domain edges and the peeling off between stacked lipid layers. These results point to the applicability of chiral packing theory in bolaamphiphilic supramolecular assemblies. Contact mode atomic force microscopy observations revealed that high order existed in the surface packing arrangement. Hexagonal and pseudorectangular packings were observed in flat and twisted regions of the ribbons, respectively, suggesting a correlation between microscopic morphologies and nanoscopic packing arrangements. The tricarboxylate functionalities of the bolaamphiphilic lipid provide a handle for the manipulation of the bisfunctional PDAs' morphology. Increasing solution pH caused the fraying of helical ribbons into nanofibers accompanied by a sharp blue-to-red chromatic transition. A dramatic change in circular dichroism spectra was observed during this process, suggesting the loss of chirality in packing. A model is proposed to account for the pH-induced morphological change and chromatic transition. The color-coded transition between two distinct microstructures would be useful in the design of sensors and other "smart" nanomaterials requiring defined molecular templates.

Acetylene↗
PubMed2003

Functional nanocomposites prepared by self-assembly and polymerization of diacetylene surfactants and silicic acid.

Conjugated polymer/silica nanocomposites with hexagonal, cubic, or lamellar mesoscopic order were synthesized by self-assembly using polymerizable amphiphilic diacetylene molecules as both structure-directing agents and monomers. The self-assembly procedure is rapid and incorporates the organic monomers uniformly within a highly ordered, inorganic environment. By tailoring the size of the oligo(ethylene glycol) headgroup of the diacetylene-containing surfactant, we varied the resulting self-assembled mesophases of the composite material. The nanostructured inorganic host altered the diacetylene polymerization behavior, and the resulting nanocomposites show unique thermo-, mechano-, and solvatochromic properties. Polymerization of the incorporated surfactants resulted in polydiacetylene (PDA)/silica nanocomposites that were optically transparent and mechanically robust. Molecular modeling and quantum calculations and (13)C spin-lattice relaxation times (T(1)) of the PDA/silica nanocomposites indicated that the surfactant monomers can be uniformly organized into precise spatial arrangements prior to polymerization. Nanoindentation and gas transport experiments showed that these nanocomposite films have increased hardness and reduced permeability as compared to pure PDA. Our work demonstrates polymerizable surfactant/silica self-assembly to be an efficient, general approach to the formation of nanostructured conjugated polymers. The nanostructured inorganic framework serves to protect, stabilize, and orient the polymer, mediate its performance, and provide sufficient mechanical and chemical stability to enable integration of conjugated polymers into devices and microsystems.

Acetylene↗
PubMed2003

Colorimetric reversibility of polydiacetylene supramolecules having enhanced hydrogen-bonding under thermal and pH stimuli.

To investigate the role of hydrogen-bonding on colorimetric transition of polydiacetylene supramolecules, novel diacetylene derivatives allowing various hydrogen-bonding states were synthesized by coupling carboxy-substituted (ortho-, meta-, and para-) anilide groups with a typical single-chain diacetylene lipid. One with a terminal carboxyl group at the meta position provided the resulting supramolecular Langmuir-Schaefer films with enhanced hydrogen-bonding, and hence resulted in unprecedented colorimetric reversibility under both thermal and pH stimuli.

Acetylene↗
PubMed2003

Polymerization of diacetylenes by hydrogen bond templated adlayer formation.

Adlayers were formed on self-assembled monolayers (SAMs) formed by alkanethiols on gold. Base SAMs exposing amide functional groups at the SAM surface were formed with 12-mercaptododecanamide. Adlayers of diacetylene-containing monomers were then formed via amide hydrogen bonding in decalin and decalin/toluene mixtures. Grazing angle FTIR, contact angle measurements, and ellipsometry suggest that these adlayer films exhibit ordering and packing similar to that of SAMs on gold. Resonance Raman spectroscopy showed that these diacetylene adlayers could be readily polymerized by exposure to UV light.

Acetylene↗
PubMed2004

Lipopolysaccharide identification with functionalized polydiacetylene liposome sensors.

The outer membrane of Gram negative bacteria contains lipopolysaccharides, which are glycolipids with carbohydrate sequences that are unique for each bacterial species and serotype. In this communication, we report a method for identifying LPS from different bacteria using an electronic tongue approach. Two functionalized polydiacetylene liposomes were used as colorimetric sensors for detecting various types of LPS. These liposomes were assayed under four different experimental conditions to generate a data set of eight colorimetric responses. This data set constitutes a unique fingerprint for each analyte and permits identification of each LPS type.

Acetylene↗
PubMed2004

Nonracemic dopant-mediated hierarchical amplification of macromolecular helicity in a charged polyacetylene leading to a cholesteric liquid crystal in water.

Here we show the first example of a helical polyacetylene that forms a lyotropic liquid crystal (LC) through a hierarchical amplification of a macromolecular helicity process in water. The macromolecular helicity with an excess of one helical sense was first induced in the positively charged polyacetylene upon complexation with an extremely small oppositely charged nonracemic dopant through electrostatic interaction in water. Subsequently, the helicity was significantly amplified in the polymer backbone as an almost perfect single-handed helix through self-assembly into supramolecular helical arrays in a lyotropic cholesteric state. The present results will allow the detection of a tiny imbalance in chiral molecules and also provide new approaches for the design of novel water-soluble helical architectures and the construction of new chiral materials in areas such as biotechnology and materials science.

Acetylene↗
PubMed2004

Macromolecular helicity induction in a cationic polyacetylene assisted by an anionic polyisocyanide with helicity memory in water: replication of macromolecular helicity.

We report the first example of the replication of macromolecular helicity. An optically active helical and anionic polyelectrolyte, the sodium salt of poly(4-carboxyphenyl isocyanide), was found to serve as the template for further helicity induction in a different polyelectrolyte with opposite charges in water, resulting in interpolymer helical assemblies with controlled helicity. The effects of the pH and salt concentration on the helicity induction were investigated.

Acetylene↗
PubMed2005

Dual memory of enantiomeric helices in a polyacetylene induced by a single enantiomer.

We report the dual memory of both the enantiomeric right- and left-handed helical conformations induced in a polyacetylene based on the temperature-stimulated helicity inversion of the polymer. The polyacetylene folds into a one-handed helix induced by noncovalent bonding interactions with a single enantiomeric amine. The induced helix underwent a reversible inversion of the helicity by temperature. The diastereomeric right- and left-handed helices obtained at different temperatures could be further memorized when the optically active amine was replaced by an achiral diamine, generating right- and left-handed helices of the mirror images of each other. Consequently, both enantiomeric helices can be produced with a high efficiency from dynamically diastereomeric helical polyacetylenes induced by a single enantiomer.

Acetylene↗
PubMed2005

Synthesis of helical polyacetylene in chiral nematic liquid crystals using crown ether type binaphthyl derivatives as chiral dopants.

A series of crown ether type binaphthyl derivatives (CEBDs) were synthesized and used as chiral dopants to induce chiral nematic (N*) liquid crystals (LCs). The twisting powers of the CEBDs for phenylcyclohexane (PCH)-derived nematic LCs were evaluated. It was found that the twisting powers of the CEBDs increased with decreasing ring size of the crown ether. Helical polyacetylenes were synthesized in the N*-LCs induced by the CEBDs. The relationship between the morphology of the helical polyacetylene and the helical structure of the N*-LC was investigated. The result showed that the interdistance between the fibril bundles of the helical polyacetylene was equal to a half-helical pitch of the N*-LC and the screw direction of the polyacetylene fibrils was opposite to that of the N*-LC.

Acetylene↗
PubMed2005

Selective detection of catecholamines by synthetic receptors embedded in chromatic polydiacetylene vesicles.

A new detection scheme for catecholamines was constructed through embedding synthetic receptors within vesicles comprising phospholipids and polydiacetylene. Fluorescence emission of the polydiacetylene was induced through specific interactions between the soluble ligands and the vesicle-incorporated hosts. The system demonstrated remarkable selectivity among structurally similar ligands and achieved much lower detection thresholds compared to that of other reported catecholamine sensors. The chromatic assembly provides a generic route for high sensitivity detection of ligand-receptor interactions.

Acetylene↗
PubMed2005

Fabrication of polydiacetylene nanowires by associated self-polymerization and self-assembly processes for efficient field emission properties.

The paper described here concerns a challenge of general interest for producing a novel structure of a polymer aggregate, the achievement of nanowires with controlled diameters. We provide a strategy for fabricating a supramolecular polymer, in which ordered polydiacetylene nanowires can be obtained by associated self-polymerization and self-assembly processes. The polymer nanowire film shows excellent field emission properties with the turn-on field of 8.2 V/mum at 10 muA/cm2 and the maximum current density of 5 mA/cm2 at an applied field of 15 V/mum.

Acetylene↗
PubMed2005

Polydiacetylene/silica nanocomposites with tunable mesostructure and thermochromatism from diacetylenic assembling molecules.

Conjugated polydiacetylene (PDA)/silica nanocomposites with tunable mesostructures and reversible thermochromatism were synthesized through self-directed assembly of diacetylenic silanes. In contrast to the previous studies, where the PDA side chains interacted weakly through noncovalent interactions, the side chains in the present nanocomposites are covalently connected to the inorganic silica frameworks, providing control over the molecular alignment, stability, and electronic properties. Furthermore, tuning the molecular architecture (e.g., the shape and side-chain length) allows control over the mesostructure (e.g., cubic and lamellar) and chromatic response of the nanocomposites (from irreversible to partially reversible and then to completely reversible). As a result of the covalent interactions, the nanocomposites also demonstrate higher reversible chromatic transition temperatures. This work not only provides responsive robust chromatic materials toward practically reusable PDA sensors but also is of great fundamental value for the design of supramolecular assembly and the understanding of the chromatic mechanism of PDA.

Acetylene↗
PubMed2005

A polydiacetylene-based fluorescent sensor chip.

Self-assembled diacetylene vesicles were spotted and immobilized on aldehyde-modified glass substrates using conventional microarray technology. Irradiation of the immobilized diacetylenes allowed generation of nonfluorescent "blue-phase" polydiacetylene (PDA) arrays. Specific interaction of the PDA vesicle arrays with carbohydrates or poly(acrylic acid) solutions afforded fluorescent profiles.

Acetylene↗
PubMed2005

Synthesis of functionalized asymmetric star polymers containing conductive polyacetylene segments by living anionic polymerization.

Novel 3-arm ABC, 4-arm ABCD, and 5-arm ABCDE asymmetric star polymers comprising the conductive polyacetylene precursor, poly(4-methylphenyl vinyl sulfoxide) (PMePVSO), and other segments, such as polystyrene, poly(alpha-methylstyrene), poly(4-methoxystyrene), poly(4-trimethylsilylstyrene), and poly(4-methylstyrene), were synthesized by the methodology based on living anionic polymerization using DPE-functionalized polymers. This methodology involves the addition reaction of a DPE-functionalized polymer to a living anionic polymer followed by the living anionic polymerization of MePVSO initiated from the in situ formed polymer anion with two, three, or four polymer segments. The resultant asymmetric star polymers possessed predetermined molecular weights, narrow molecular weight distributions (Mw/Mn < 1.03), and desired compositions as confirmed by SEC, 1H NMR, SLS, and elemental analysis. After thermal treatment, the PMePVSO segment in the star polymer could be completely converted into a conductive polyacetylene segment, evident from TGA and elemental analysis. These asymmetric star polymers are expected to exhibit interesting solution properties and unique microphase-separated morphological suprastructures with potential applications in nanoscopic conductive materials. Moreover, this methodology can afford the target asymmetric star polymers with arm segments varying in a wide range and enables the synthesis of more complex macromolecular architectures.

Acetylene↗
PubMed2006

Responsive periodic mesoporous polydiacetylene/silica nanocomposites.

Responsive PMO materials have been synthesized through co-assembly of bridged diacetylenic silsesquioxane and surfactant. The spatially defined polydiacetylenic component, mesoporous network, and the covalent proximity of polydiacetylene to silica endow the PMO with mechanical robustness, reversible chromatic responses, improved thermal stability, and faster responses to chemical stimuli. This research also provides an efficient molecular design and assembly paradigm to fabricate a family of conjugated optoelectronic materials, creating novel platforms for sensors, actuators, and other device applications.

Nanocomposites↗
PubMed2006

Color fingerprinting of proteins by calixarenes embedded in lipid/polydiacetylene vesicles.

"Naked eye" color detection of proteins was achieved by embedding calixarene receptors within vesicles comprising phospholipids and the chromatic polymer polydiacetylene. Dramatic visible absorbance changes were induced through electrostatic interactions between the protein surface and the vesicle-incorporated hosts. The colorimetric responses could be induced by micromolar protein concentrations, and furthermore, specific protein fingerprints could be obtained by incorporating different receptors within the vesicles. Fluorescence and circular dichroism experiments confirmed the relationship between the colorimetric phenomena and protein docking on the surface of the chromatic vesicles. The colorimetric assay constitutes a generic platform for high-sensitivity detection of soluble proteins and for evaluation of protein surface charge distribution.

Calixarenes↗
PubMed2005

Polyacetylenic compounds, ACAT inhibitors from the roots of Panax ginseng.

Acyl-CoA: cholesterol acyltransferase (ACAT), which plays a role in the absorption, storage, and production of cholesterol, has been explored as a potential target for pharmacological intervention of hyperlipidemia and atherosclerotic disease. In our search for ACAT inhibitors from natural sources, the petroleum ether extract of Panax ginseng showed moderate inhibition of ACAT enzyme from rat liver microsomes. Bioactivity-guided fractionations led to the isolation of one new polyacetylenic compound, (9R,10S)-epoxy-16-heptadecene-4, 6-diyne-3-one (1), in addition to the previously reported polyacetylenic compounds 2 and 3. Their chemical structures were elucidated on the basis of spectroscopic evidence (UV, IR, NMR, and MS). The compounds 1, 2, and 3 showed significant ACAT inhibition with IC(50) values of 35, 47, and 21 microM, respectively.

Acetylene↗
PubMed2005

Polyacetylenes from the Apiaceae vegetables carrot, celery, fennel, parsley, and parsnip and their cytotoxic activities.

A dichloromethane extract of root celery yielded falcarinol, falcarindiol, panaxydiol, and the new polyacetylene 8-O-methylfalcarindiol. The structure of the new compound was established by one- and two-dimensional (1D and 2D) NMR, mass spectrometry, and optical rotation data. Nonpolar extracts of roots and bulbs of carrots, celery, fennel, parsley, and parsnip were investigated for their content of polyacetylenes by high-performance liquid chromatography with diode array detection (HPLC-DAD). All five species contained polyacetylenes, although carrots and fennel only in minor amounts. Additionally, the cytotoxicity of the four polyacetylenes against five different cell lines was evaluated by the annexin V-PI assay. Falcarinol proved to be the most active compound with a pronounced toxicity against acute lymphoblastic leukemia cell line CEM-C7H2, with an IC(50) of 3.5 micromol/L. The possible chemopreventive impact of the presented findings is discussed briefly.

Acetylene↗