PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Polyacetylene Polymer”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6Linked to original sources
PubMed1997

Antimicrobial activity of polyacetylenes from Bellis perennis and their synthetic derivatives.

The chemical investigation of the essential oils from the aerial organs of Bellis perennis L., the common daisy, showed that polyacetylenes were one of the dominant class of compounds. The major constituents, methyl deca-4,6-diynoate and deca-4,6-diynoic acid, and their structural analogues, deca-4,6-diyne, dimethyl octa-3,5-diyne-1,8-dioate and deca-4,6-diyne-1,10-dioic acid, were synthesised and their antimicrobial activity evaluated. Only deca-4,6-diynoic acid and deca-4,6-diyne-1,10-dioic acid showed antimicrobial activity, being the two compounds mainly effective against Gram-positive and Gram-negative bacteria, respectively. Structure-activity relationships of the tested polyacetylenes are discussed.

Acetylene↗
PubMed2002

Quantum bits with polyacetylene.

The dynamics of a polyacetylene single chain as a system for possible physical implementations of quantum bits is determined. This novel proposition is studied by varying intensity and duration of application of an electric field as well as the intensity, number, and position in the polymer chain of impurity molecules. The behavior of soliton pairs, whose associated energy levels form the quantum bit, is analyzed. The chain is modeled by a modified Pariser-Parr-Pople Hamiltonian extended to include the effects of an external electric field and the parameters of the impurity molecules. The effect of the variation of the field and impurities on the separation of the energy levels associated with soliton pairs is analyzed by numerical integration of the equations of motion. Two different approaches for controlling the separation of levels are presented, and their features compared. First, the use of changes in the electric field to control the distance (and ultimately coupling) between two solitons moving freely on the chain or captured by the potential generated by the impurity molecules. Second, the change in the intensity of the impurities alone, with no application of an external field. We have found that the effect of the use of the field on the separation of levels is much smaller than the one obtained by changes in the parameters of the impurity molecules, which eventually led us to achieve quantum bit behavior in a polyacetylene chain. The influence of the field and impurity parameters in the energy levels is determined, as well as their role in the coupling of the two solitons on the chain. Critical values for distance between solitons, intensity of field, and impurities that determine whether a pair of solitons can work as a quantum bit are obtained.

Journal Article↗
PubMed2003

Polyacetylenes in hairy roots of a panax hybrid.

From the hairy roots of an interspecific hybrid ginseng ( Panax ginseng x P. quinquefolium) known as Pgq, three polyacetylenes were isolated: panaxynol, panaxydol and 1,8-heptadecadiene-3,10-diol. These compounds isolated from the hairy roots were used for quantitative analysis to investigate the polyacetylene production of the hairy roots cultured in Gamborg B5 (B5) and 1/8 Murashige-Skoog (MS) liquid media. Maximum growth of the hairy roots was observed (ca. 5.4 g fresh weight/100 mL flask) at 8 weeks of culture in B5 medium. The highest total content of total polyacetylenes was 0.18 % of dry weight at week 8 when cultured in 1/8 MS medium. In addition, we compared the yields of polyacetylenes and ginsenosides in hairy roots cultured in B5 with those in 1/8 MS media and found the highest yields were obtained in the hairy roots cultured in B5 medium (1.24 mmol/flask polyacetylenes and 4.45 mmol/flask ginsenosides at week 8).

Acetylene↗
PubMed2003

Polyacetylene glycosides from Pratia nummularia cultures.

Two polyacetylene glycosides, lobetyol 9-O-glc(6)-(1)rha (pratialin-A) and lobetyol 9-O-glc(6)-(1)glc(6)-(1)glc (pratialin-B), were isolated from Pratia nummularia (Campanulaceae) callus and hairy root cultures and their chemical structures were determined by analysis of spectroscopic data. From the methanol extract of the hairy root cultures, together with the known polyacetylene constituents lobetyol, lobetyolin, and lobetyolinin, tryptophan was also isolated. This report is the first example of the isolation and structure elucidation of rutinoside (pratialin-A) and triglucoside (pratialin-B) derivatives of polyacetylene constituents.

Acetylene↗
PubMed2004

Importance of chain-chain interactions on the band gap of trans-polyacetylene as predicted by second-order perturbation theory.

We employ the Laplace-transformed second-order Moller-Plesset perturbation theory for periodic systems in its atomic orbital basis formulation to determine the geometric structure and band gap of interacting polyacetylene chains. We have studied single, double, and triple chains, and also two-dimensional crystals. We estimate from first principles the equilibrium interchain distance and setting angle, along with binding energy between trans-polyacetylene chains due to dispersion interactions. The dependence of the correlation corrected quasiparticle band gap on the intrachain and interchain geometric parameters is studied, obtaining that the gap of the compound structures is substantially reduced with respect to the single chain polymer.

Journal Article↗
PubMed2005

Second-order Møller-Plesset evaluation of the bond length alternation of several series of linear oligomers.

We investigate, at the second-order Møller-Plesset level, the bond length alternation of 30 series of increasingly long linear oligomers for a total of more than 250 compounds, polyacetylene, polymethineimine, polyphosphinoborane, polyaminoborane, polyphosphazene, etc., for which, often for the first time, an accurate estimate of the polymeric bond length alternation is given. The variations induced either by chemical substitution of the backbone atoms or conformational modifications are discussed. Only three polymers present a large bond length alternation (>0.03 A). Systematic basis set effects have been unravelled, i.e., MP2/6-311G(2d) always overshoots the bond length alternation. Best estimates of the bond length alternation are provided for more than a dozen of polymers.

Journal Article↗
PubMed2006

Functional perovskite hybrid of polyacetylene ammonium and lead bromide: Synthesis, light emission, and fluorescence imagining.

A highly photoresponsive perovskite hybrid containing an electroactive organic component (H1) was fabricated. A disubstituted polyacetylene (PA) with a hidden amino functionality (P3) was synthesized, hydrolysis and quaternization of which afforded the desired PA ammonium salt (P5). Mixing P5 with lead bromide readily yielded H1, which was stable, soluble, and film-forming. The inorganic framework induced the polymer chains to align in an ordered fashion, which helped to populate the chain segments with long conjugation lengths. The hybrid emitted a blue light (457 nm) in a high quantum yield (62%), thanks to the enhanced electronic conjugation, the weakened interaction between the layer-segregated chains, and the efficient energy transfer from the inorganic sheets to the organic layers. P3 exhibited a half-discharge time as short as approximately 0.7 s, representing the first example of an efficient photoconductive disubstituted PA. While stable to normal light illumination, H1 was rapidly bleached upon exposure to high-power UV irradiation, enabling facile generation of two-dimensional luminescent photopatterns. After the UV irradiation, the emissions of P9 and P9/H12 were enhanced and weakened, respectively, proving that the inorganic perovskite framework works as a photocatalyst for accelerating the bleaching process of the conjugated PA chains.

Journal Article↗
PubMed2004

New evidences of antimalarial activity of Bidens pilosa roots extract correlated with polyacetylene and flavonoids.

Bidens pilosa is among the several plants used in Brazil to treat malaria. It was demonstrated that crude extracts from roots prepared with 80% ethanol by percolation are active in vitro against Plasmodium falciparum and the activity is correlated with the presence of polyacetylene and flavonoids. This extract was submitted to column chromatography with ether and ether methanol (1:1) and two fractions, enriched in polyacetylene and flavonoids, respectively, were obtained. The extract and the fractions were assessed by HPLC/DAD analysis and antimalarial tests in vivo. Ethanol extract showed by HPLC the presence of several peaks for polyacetylene and flavonoids, compounds corresponding to quercetin-3,3'-dimethoxy-7-0-rhamnoglucopyranose and the acetylene 1-phenyl-1,3-diyn-5-en-7-ol-acetate, previously identified in this extract. The peaks for flavonoids were absent in ether fraction and those ones for polyacetylene in ether:methanol. In in vivo tests, ethanol extract caused 36% of reduction of parasitaemia at fifth day, and 29% at seventh day. Ether:methanol fraction caused 38% of reduction at fifth day but was inactive at day 7. The survival of the animals treated with 80% ethanol extract was higher than in the fractions. The results showed that the in vivo activity of ethanol extract depends on the presence of polyacetylene and flavonoids.

Acetylene↗
PubMed2006

Combinatorial search for optimal hydrogen-storage nanomaterials based on polymers.

We perform an extensive combinatorial search for optimal nanostructured hydrogen-storage materials among various metal-decorated polymers using first-principles density-functional calculations. We take into account the zero-point vibration as well as the pressure- and temperature-dependent adsorption-desorption probability of hydrogen molecules. An optimal material we identify is Ti-decorated cis-polyacetylene with reversibly usable gravimetric and volumetric density of 7.6 wt % and 63 kg/m(3), respectively, near ambient conditions. We also propose "thermodynamically usable hydrogen capacity" as a criterion for comparing different storage materials.

Journal Article↗
PubMed1998

Antiproliferative constituents in Umbelliferae plants II. Screening for polyacetylenes in some Umbelliferae plants, and isolation of panaxynol and falcarindiol from the root of Heracleum moellendorffii.

Methanol extracts of 36 samples of 21 Umbelliferae plants were screened for polyacetylenic compounds using the ELISA for panaxytriol, and their antiproliferative activity was checked by MTT assay using the tumor cell lines MK-1, HeLa and B16F10. The presence of antiproliferative polyacetylenes was suggested in Angelica acutiloba (fruit), Anethum graveolens (root), Bupleurum rotundifolium (fruit), Carum carvi (fruit and root), Coriandrum sativum (fruit), Cryptotaenia japonica (leaf), Glehnia littoralis (fruit), Heracleum moellendorffii (root) and Torilis japonica (fruit). Panaxynol and falcarindiol were successfully isolated from the root of Heracleum moellendorffii as antiproliferative polyacetylenes.

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↗
PubMed2001

Rapid fabrication of three-dimensional porous films with biomimetic patterns by natural evaporation of amphiphilic polyacetylene solutions under ambient conditions.

A simple process for fast fabrication of thin films with biomimetic morphological structures from a group of linear homopolymers is developed. Natural evaporation of tetrahydrofuran, chloroform, and hexane-dichloromethane solutions of poly(phenylacetylene)s that contain amino acid and ethylene glycol moieties under ambient conditions instantly produces three-dimensional porous films with structural patterns reminiscent of honeycombs and radiolarian shells. Morphological analysis by optical and electronic microscopy suggests that vesicles of the amphiphilic polymers serve as building blocks in the self-organization to the biomimetic structures.

Acetylene↗
PubMed2006

Isolation and structure elucidation of cytotoxic polyacetylenes and polyenes from Echinacea pallida.

Bioassay-guided fractionation of n-hexane extracts of Echinacea pallida (Asteraceae) roots led to the isolation and structure elucidation of two polyacetylenes (1, 3) and three polyenes (2, 4, 5). Two are known hydroxylated compounds, namely 8-hydroxy-pentadeca-(9E)-ene-11,13-diyn-2-one (1) and 8-hydroxy-pentadeca-(9E,13Z)-dien-11-yn-2-one (2). Two dicarbonylic constituents, namely pentadeca-(9E)-ene-11,13-diyne-2,8-dione (3) and pentadeca-(9E,13Z)-dien-11-yne-2,8-dione (4), were isolated and characterized for the first time. Furthermore, the structure elucidation of pentadeca-(8Z,13Z)-dien-11-yn-2-one (5) is described. The structure of the compounds isolated was determined on the basis of UV, IR, NMR (including 1D and 2D NMR experiments, such as 1H-1H gCOSY, gHSQC-DEPT, gHMBC, gNOESY) and MS spectroscopic data. The cytotoxic activity of the isolated constituents against MIA PaCa-2 human pancreatic adenocarcinoma cells was evaluated in the concentration range 1-100 microg/ml. Results show that the hydroxylated compounds (1, 2) have low cytotoxicity, while the more hydrophobic polyacetylenes (3) and polyenes (4, 5) displayed moderate activity.

Acetylene↗
PubMed2005

Properties of polythiophene and related conjugated polymers: a density-functional study.

Using a parameter-free, density-functional method that has been developed explicitly for the theoretical treatment of infinite, periodic, isolated, helical polymers we study various polymers related to polythiophene. In particular we discuss how the electronic properties of polythiophene are changed when replacing some of the H atoms by CH3 group, by incorporating vinylene bridges into the backbone, or when replacing some or all the CH units of the backbone by N atoms. We observe the weakest effects for the methyl-substitution and the strongest for the N-incorporation. The latter leads to an overall downward shift of all bands, but in contrast to the case for polyacetylene, the unrelaxed compound with N atoms does not have N lone-pair orbitals as the highest occupied ones. Instead these occur at somewhat deeper energies. When comparing the aromatic and quinoid forms we found for the pure compound as well as for the methyl-containing one that the gap closes when passing from the one to the other form which was not found for any of the other materials of the present study. Moreover, the energy of the HOMO was found to depend stronger on the bond-length alternation than the energy of the LUMO, ultimately giving that polarons will induce two asymmetrically placed gap states with the energetically lower one appearing deeper in the gap than the other one.

Hydrogen↗
PubMed2003

Determination of polyacetylenes and ginsenosides in Panax species using high performance liquid chromatography.

A new HPLC method was developed to separate and identify three polyacetylenes (panaxynol, panaxydol and 1,8-heptadecadiene-4,6-diyne-3,10-diol) found in Panax species. The mobile phase was a linear gradient of 2 : 1 : 3 to 2 : 1 : 1 (v/v/v) methanol/acetonitrile/water in 40 min. HPLC analysis was performed at a flow rate of 1.5 ml/min with UV detection at 254 nm. The contents of the polyacetylenes and ginsenosides in Panax ginseng (white ginseng and red ginseng), P. quinquefolium, P. japonicus, and P. noteginseng were determined using these methods. The species containing the highest polyacetylene content (0.080%) was P. quinquefolium cultivated in Nagano, Japan. Meanwhile, the species with the highest ginsenoside content (9.176%) was P. noteginseng cultivated in Yunnan, China.

Acetylene↗
PubMed2005

Functional polyacetylenes.

Polyacetylene (PA) is a Nobel Prize-winning macromolecule. In this work, PA is molecularly functionalized, which endows it with an array of new functional properties. The molecular functionalization is realized by attachment of functional pendants to the polyene backbone. Our efforts in the catalyst exploration and reaction optimization have led to the syntheses of a large number of PA derivatives carrying functional groups. Polymer reactions are exploited as an alternative route to the functional PAs that are difficult or impossible to access by direct polymerizations of their monomers. The new PAs with appropriate backbone-pendant combinations show various functional properties such as liquid crystallinity, photoconductivity, light emission, ionic susceptibility, photoresistance, chromism, helical chirality, optical nonlinearity, self-assembly, cytocompatibility, and bioactivity. The properties of the PAs are tuned internally and manipulated externally: the former is achieved by changing their molecular structures, especially their functional pendants, while the latter is accomplished by applying thermal, mechanical, electrical, photonic, and chemical stimuli.

Acetylene↗