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PubMed2005

Supramolecular electronics; nanowires from self-assembled pi-conjugated systems.

The conditions required for supramolecular electronics, e.g. nano-sized optoelectronic devices, will be illustrated on the basis of the programmed self-assembly of pi-conjugated systems into individual nanosized wires. Using the supramolecular design rules nanowires can be created from almost any polymeric and oligomeric pi-conjugated system. In the case of oligomers it is even possible to construct individual wires having a uniform diameter of one molecule thickness. The construction of wires on a substrate is possible by self-assembly in solution or during the deposition. The transfer of the supramolecular stacks from solution to a solid support is a very delicate process. A comprehensive knowledge of all intermolecular interactions gives rise to controlled transfer of pi-conjugated assemblies to specific surfaces. There are a large number of very appealing targets that should be reached before supramolecular electronics can serve as an attractive alternative in between single molecule electronics and bulk devices. Nevertheless, the combination of exciting scientific results and intriguing technological challenges creates an interesting future for supramolecular electronics.

Dendrimers↗
PubMed2005

Poly(diacetylene)-nanofibers can be fabricated through photo-irradiation using natural polysaccharide schizophyllan as a one-dimensional mold.

Schizophyllan interacts with various 1,4-diphenylbutadiyne derivatives to induce their chirally-twisted packing. A series of referential experiments using other polysaccharides (amylose, pullulan, dextran, etc.) and a carbohydrate-appended detergent (dodecyl-beta-d-glucopyranoside) indicates that these 1,4-diphenylbutadiyne derivatives are accommodated within a tubular cavity constructed by a helical superstructure of schizophyllan. In these 1,4-diphenylbutadiyne derivatives, 1,4-bis(p-propionamidophenyl)butadiyne can be easily polymerized through UV-irradiation, in which schizophyllan acts as a one-dimensional mold to produce the corresponding poly(diacetylene)s with fibrous morphologies. Detailed investigations on this unique approach to prepare the nanofibers revealed that it includes two individual processes, that is, 1) UV-mediated polymerization of encapsulated 1,4-bis(p-propionamidophenyl)butadiyne to produce immature nanofibers and 2) their reorganization through hydrophobic interfiber interactions into ordered nanofibers. The other 1,4-diphenylbutadiyne derivatives could not be polymerized through UV-irradiation, indicating that the p-propionamido-functionalities play substantial roles for a suitable packing of the monomer for the polymerization. The other 1,4-diphenylbutadiyne derivatives, however, can be also polymerized through gamma-ray irradiation in the presence of schizophyllan to give the corresponding poly(diacetylene)-nanofibers, emphasizing the wide applicability of the schizophyllan-based strategy for polymerization of various 1,4-diphenylbutadiyne derivatives.

Acetylene↗
PubMed2002

Mode of inhibition of HIV-1 reverse transcriptase by polyacetylenetriol, a novel inhibitor of RNA- and DNA-directed DNA polymerases.

Polyacetylenetriol (PAT), a natural marine product from the Mediterranean sea sponge Petrosia sp., was found to be a novel general potent inhibitor of DNA polymerases. It inhibits equally well the RNA- and DNA-dependent DNA polymerase activities of retroviral reverse transcriptases (RTs) (i.e. of HIV, murine leukaemia virus and mouse mammary tumour virus) as well as cellular DNA polymerases (i.e. DNA polymerases alpha and beta and Escherichia coli polymerase I). A study of the mode and mechanism of the polymerase inhibition by PAT has been conducted with HIV-1 RT. PAT was shown to be a reversible non-competitive inhibitor. PAT binds RT independently and at a site different from that of the primer-template and dNTP substrates with high affinity (K(i)=0.51 microM and K(i)=0.53 microM with dTTP and with dGTP as the variable substrates respectively). Blocking the polar hydroxy groups of PAT has only a marginal effect on the inhibitory capacity, thus hydrophobic interactions are likely to play a major role in inhibiting RT. Preincubation of RT with the primer-template substrate prior to the interaction with PAT reduces substantially the inhibition capacity, probably by preventing these contacts. PAT does not interfere with the first step of polymerization, the binding of RT to DNA, nor does the inhibitor interfere with the binding of dNTP to RT/DNA complex, as evident from the steady-state kinetic study, whereby K(m) remains unchanged. We assume, therefore, that PAT interferes with subsequent catalytic steps of DNA polymerization. The inhibitor may alter the optimal stereochemistry of the polymerase active site relative to the primer terminus, bound dNTP and the metal ions that are crucial for efficient catalysis or, alternatively, may interfere with the thumb sub-domain movement and, thus, with the translocation of the primer-template following nucleotide incorporation.

Acetylene↗
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↗
PubMed2004

New Polyacetylenes, DGAT inhibitors from the roots of Panax ginseng.

The petroleum ether extract of Panax ginseng showed a significant inhibition of the diacylglycerol acyltransferase (DGAT) enzyme from rat liver microsomes. Bioactivity-guided fractionation led to the isolation of two new polyacetylenic compounds, (9 R,10 S)-epoxyheptadecan-4,6-diyn-3-one ( 1) and 1-methoxy-(9 R,10 S)-epoxyheptadecan-4,6-diyn-3-one ( 2). Their chemical structures were elucidated on the basis of spectroscopic evidence and asymmetric synthesis. IC50 values of 9 microg/mL ( 1) and 32 microg/mL ( 2) were obtained.

Acetylene↗
PubMed2004

Polyacetylenic compounds and butanol fraction from Bidens pilosa can modulate the differentiation of helper T cells and prevent autoimmune diabetes in non-obese diabetic mice.

Compelling evidence suggests that infiltrating CD4+ type I helper T (Th1) cells in the pancreatic islets play a pivotal role in the progression of diabetes in non-obese diabetic (NOD) mice. We demonstrate in the present report that a butanol fraction of B. pilosa suppressed the development of diabetes, helped maintain levels of blood sugar and insulin in NOD mice in a dose-dependent manner and elevated the serum IgE levels regulated by Th2 cytokines in NOD mice. Moreover, the butanol fraction inhibited the differentiation of naive helper T (Th0) cells into Th1 cells but enhanced their transition into type II helper T (Th2) cells using an in vitro T cell differentiation assay. Two polyacetylenic compounds, 2-beta-D-glucopyranosyloxy-1-hydroxy-5(E)-tridecene-7,9,11-triyne and 3-beta-D-glucopyranosyloxy-1-hydroxy-6(E)-tetradecene-8,10,12-triyne, identified from the butanol fraction also prevented the onset of diabetes like the butanol fraction. The latter compound showed a stronger activity for T cell differentiation than the former. In summary, the butanol fraction of B. pilosa and its polyacetylenes can prevent diabetes plausibly via suppressing the differentiation of Th0 cells into Th1 cells and promoting that of Th0 cells into Th2 cells.

Acetylene↗
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↗
PubMed1997

Polyacetylene analogs, isolated from hairy roots of Panax ginseng, inhibit Acyl-CoA : cholesterol acyltransferase.

In the course of our screening program for acyl-CoA : cholesterol acyltransferase (ACAT) inhibitors from Korean herbal medicines, ACAT inhibitors were isolated from the hairy roots of Panax ginseng (Araliaceae) and identified as panaxynol, panaxydol, panaxydiol, and panaxytriol. These active compounds inhibit rat liver ACAT with IC50 values of 94, 80, 45 and 79 microM, respectively.

Acetylene↗
PubMed1994

Anti-inflammatory active polyacetylenes from Bidens campylotheca.

The n-hexane extract of Bidens campylotheca Schultz Bip. ssp campylotheca (Compositae) showed significant in vitro inhibition of cyclooxygenase (CO) and 5-lipoxygenase (5-LO). Five polyacetylenes, heptadeca-2E,8E,10E,16-tetraene-4,6-diyne (1), heptadeca-2E,8Z,10E,16-tetraene-4,6-diyne (2), heptadeca-2E,8E,16-triene-4,6-diyne-10-ol (3), safynol (5) and, as a new compound, safynol-2-O-isobutyrate (4) could be isolated and their structures elucidated mainly by UV, MS, NMR, and COSY-NMR. The isolated compounds exhibited a significant inhibitory effect on cyclooxygenase and 5-lipoxygenase.

Acetylene↗
PubMed1989

The complex nature of the mechanism of toxicity of antibiotic dithiacyclohexadiene polyines (thiarubrines) from the asteraceae.

Thiarubrine A, a dithiacyclohexadiene polyine from the roots of Chaenactis douglasii, and a related dithiacyclohexadiene from Rudbeckia hirta exhibit strong light-independent antibacterial and antifungal activity. This activity is enhanced by exposure to visible light. Visible light also converts the compounds to the corresponding thiophenes. These are antibiotic only when irradiated with UV-A. Dithiacyclohexadienes are the first polyines to exhibit such complex mechanisms of toxicity towards microorganisms.

Alkynes↗
PubMed2006

Multiple self-localized electronic states in trans-polyacetylene.

Electronic structure calculations on a conjugated polymer chain by Hartree-Fock and density functional theory show a sequence of self-localized states, which stand in contrast to the single self-localized soliton state described by the Su-Schrieffer-Heeger model Hamiltonian. An extended Hubbard model, which treats electron-electron interactions up to second neighbors, is constructed to demonstrate that the additional states arise from a strong band-bending effect due to the presence of localized electric fields of charged solitons. We suggest the optical response of these electronic states may be associated with the near-edge oscillations observed in photo-induced absorption spectra. Our calculations indicate further that in the presence of counterions, the additional localized states continue to exist. Implications regarding soliton mobility and high-resolution ion sensing are briefly discussed.

Acetylene↗
PubMed2001

Absolute stereochemistry and anti-HIV activity of minquartynoic acid, a polyacetylene from Ochanostachys amentacea.

Anti-HIV bioassay-guided fractionation of an organic extract of Ochanostachys amentacea provided an HIV-inhibitory polyacetylenic acid. The identity of this compound was established as (-)-17-hydroxy-9,11,13,15-octadecatetraynoic acid (1), also known as minquartynoic acid, by comparison of its physical and spectral data with previously reported values. Analysis of Mosher's ester derivatives of the methyl ester of 1 allowed assignment of S absolute stereochemistry to the lone chiral center. In an in vitro XTT-based anti-HIV assay, 2-5 micrograms/mL of minquartynoic acid (1) effectively inhibited human lymphoblastoid cell killing by HIV-1.

Alkynes↗