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At least 73 records · Page 4Linked to original sources
PubMed2003

trans-Bis[1,2-bis(diphenylphosphino)ethane-kappa(2)P,P']bis[4-(trimethylsilyl)buta-1,3-diynyl]ruthenium(II) and trans-bis[1,2-bis(diphenylphosphino)ethane-kappa(2)P,P']bis(buta-1,3-diynyl)ruthenium(II).

The crystal structures of the title compounds, [Ru(C(7)H(9)Si)(2)(C(26)H(24)P(2))(2)] and [Ru(C(4)H)(2)(C(26)H(24)P(2))(2)], are described. The metal centre in both complexes has an octahedral coordination geometry, with mutually trans buta-1,3-diynyl ligands forming pseudo-linear ruthenium-centred polyyne chains.

Journal Article↗
PubMed2006

Fe/C interactions during SWNT growth with C2 feedstock molecules: A quantum chemical molecular dynamics study.

We are presenting the first quantum chemical molecular dynamics (QM/MD) model simulations for iron catalyzed single-walled carbon nanotube (SWNT) growth based on the density functional tight binding (DFTB) quantum chemical potential. As model systems, open-ended (10,10) armchair tube fragments were selected with 0, 10, and 20 Fe atoms attached in 1,4-positions on the open rims, and ensembles of randomly oriented C2 molecules were included to simulate carbon plasma feedstock molecules. Isokinetic trajectories at 1500 K to 3000 K show that divalent Fe increases the number of coordination partners with carbon and/or Fe, depending on the Fe concentration. Fe/C interactions weaken the tube sidewall due to electron transfer from Fe into antibonding carbon orbitals, and C2 addition occurs mainly in an Fe-C2-Fe bridge addition mechanism, while growth of polyyne chains characteristic for high-temperature carbon systems is suppressed in the presence of Fe on the rims of the growing SWNT. Our findings are the first quantum chemical evidence for the importance of intermetallic interactions during SWNT growth.

Carbon↗
PubMed1999

A review of the volatile metabolites of fungi found on wood substrates.

The holdings of eight collections of fungi have been examined for organisms isolated from wood and/or trees. Further selection of these fungi has been made according to their reported ability to produce volatile, biologically active metabolites. It is emphasized that the isolates in the collections do not necessarily produce such metabolites. The list of fungi fulfilling these conditions is slightly augmented by reports we have found in the literature, where the fungi concerned have not yet been deposited. The biochemistry of these compounds is considered with particular emphasis on their biosynthesis including that by Homo sapiens. The physiological and toxicological activity of these metabolites is reviewed especially with reference to their potential role in the complex symbioses existent in, for example, a tree. The review concludes with a discussion of areas of botany deserving increased attention in the hope that this will stimulate further work. The statements in the review are based on 173 references.

Acetylene↗
PubMed2004

Chiral amplification in macromolecular helicity assisted by noncovalent interaction with achiral amines and memory of the helical chirality.

Poly[(4-carboxyphenyl)acetylene] (poly-1) exhibits an intense induced circular dichroism (ICD) in the UV-visible region upon complexation with excess (R)-1-(1-naphthyl)ethylamine ((R)-2), owing to the formation of a predominantly single-handed helical conformation of the polymer backbone. In the presence of a small amount of (R)-2, poly-1 showed a very weak ICD due to the lack of a single-handed helical conformation. However, we have found that the co-addition of the excess bulky, achiral 1-naphthylmethylamine (5) with a small amount of (R)-2 caused a dramatic increase in the ICD magnitude, comparable to the full ICD induced by excess (R)-2. This indicates that an almost single-handed helix can be induced on poly-1 upon complexation with a small amount of (R)-2 assisted by achiral 5. Furthermore, the induced single-handed helical poly-1 could be successfully memorized by the replacement of (R)-2 and 5 with achiral 2-aminoethanol or n-butylamine.

Acetylene↗
PubMed2005

Energy and electron transfer in polyacetylene-linked zinc-porphyrin-[60]fullerene molecular wires.

The synthesis and electrochemical and photophysical studies of a series of alkyne-linked zinc-porphyrin-[60]fullerene dyads are described. These dyads represent a new class of fully conjugated donor-acceptor systems. An alkynyl-fullerene synthon was synthesized by a nucleophilic addition reaction, and was then oxidatively coupled with a series of alkynyl tetra-aryl zinc-porphyrins with 1-3 alkyne units. Cyclic and differential pulse voltammetry studies confirmed that the porphyrin and fullerene are electronically coupled and that the degree of electronic interaction decreases with increasing length of the alkyne bridge. In toluene, energy transfer from the excited zinc-porphyrin singlet to the fullerene moiety occurs, affording fullerene triplet quantum yields of greater than 90 %. These dyads exhibit very rapid photoinduced electron transfer in tetrahydrofuran (THF) and benzonitrile (PhCN), which is consistent with normal Marcus behavior. Slower rates for charge recombination in THF versus PhCN clearly indicate that charge-recombination events are occurring in the Marcus inverted region. Exceptionally small attenuation factors (beta) of 0.06+/-0.005 A(-1) demonstrate that the triple bond is an effective mediator of electronic interaction in zinc-porphyrin-alkyne-fullerene molecular wires.

Acetylene↗
PubMed2001

Lembehyne A, a spongean polyacetylene, induces neuronal differentiation in neuroblastoma cell.

Lembehyne A (LB-A), a spongean polyacetylene, induced neuronal cell differentiation in a neuroblastoma cell line, Neuro 2A. The LB-A treatment of Neuro 2A cells predominantly resulted in a morphological change with bipolar neurites. The acetylcholinesterase activity of Neuro 2A was also increased by the treatment of LB-A. Furthermore, the cell cycle of Neuro 2A cells was found to be specifically blocked at the G1 phase by LB-A. The structure-activity relationship study using the LB-A analogues revealed the importance of the terminal 1-yn-3-ol and unsaturated long-chain alkyl moieties for the neuronal differentiation activity of LB-A.

Acetylcholinesterase↗
PubMed1985

Thiarubrine A, a bioactive constituent of Aspilia (Asteraceae) consumed by wild chimpanzees.

Two African species of Aspilia (Asteraceae), which are used medicinally by man and which are eaten by wild chimpanzees in an unusual manner, were found to contain the potent antibiotic thiarubrine A as a major leaf phytochemical. Its presence in leaf material strengthens the view that the feeding behavior of wild chimpanzees is related to special physiological or pharmacological effects on the animals.

Alkynes↗
PubMed2003

A polyacetylene and flavonoids from Cirsium rhinoceros.

Cirsium rhinoceros Nakai (Compositae) is a herbaceous perennial native to Korea, whole plant of which has been used in folklore medicine. C. rhinoceros was extracted by a standard extraction procedure. Its n-hexane, CHCl3 and n-BuOH extracts were fractionated by column chromatography to provide a polyacetylene, a coumarin and five flavonoids. Ciryneol C, scopoletin, acacetin, cirsimarin were isolated for the first time from this plant.

Acetylene↗
PubMed2003

In vitro anti-inflammatory and pro-aggregative effects of a lipid compound, petrocortyne A, from marine sponges.

(3 S,14 S)-Petrocortyne A, a lipid compound (a C(46) polyacetylenic alcohol), from marine sponges ( Petrosia sp.) is potently cytotoxic against several solid tumour cells. In this study, we investigated in vitro anti-inflammatory and pro-aggregative effects of petrocortyne A at non-cytotoxic concentrations on various cellular inflammatory phenomena using the macrophage and monocytic cell lines RAW264.7 and U937. Petrocortyne A blocked tumour necrosis factor-alpha (TNF-alpha) production strongly and concentration-dependently in lipopolysaccharide (LPS)-activated RAW264.7 cells and phorbol 12-myristate 13-acetate (PMA)/LPS-treated U937 cells. It also blocked NO production concentration-dependently in LPS- or interferon (IFN)-gamma-treated RAW264.7 cells. Among the migration factors tested, the compound selectively blocked the expression of hepatocyte growth factor/scatter factor (HGF/SF). On the other hand, as assessed by a cell-cell adhesion assay, petrocortyne A did not block the activation of adhesion molecules induced by aggregative antibodies to adhesion molecules, but suppressed PMA-induced cell-cell adhesion significantly. Intriguingly, petrocortyne A induced U937 homotypic aggregation following long exposure (2 and 3 days), accompanied by weak induction of pro-aggregative signals such as tyrosine phosphorylation of p132 and phosphorylation of extracellular signal-related kinase 1 and 2 (ERK 1/2). Petrocortyne A may thus inhibit cellular inflammatory processes and immune cell migration to inflamed tissue.

Acetylene↗
PubMed2005

Colorimetric detection of oligonucleotides using a polydiacetylene vesicle sensor.

A new system for the colorimetric detection of oligonucleotides was developed using polydiacetylene vesicles, which play the dual role of an indicator of color transition and an amplification tag. The results are of significance in understanding the mechanism of color transition of biological recognition in polydiacetylene systems and in designing new biosensors.

Biosensing Techniques↗
PubMed2002

Anthocyanins protect light-sensitive thiarubrine phototoxins.

Thiarubrines are phototoxic plant pigments that decompose to thiophenes when exposed to sunlight. We investigated the mechanism of thiarubrine photoprotection in Ambrosia chamissonis (Less.) Greene (Asteraceae), which contains high amounts of these chemicals in its stems and leaf petioles. Thiarubrines are compartmentalized in laticifers that are surrounded by anthocyanin-containing cells. When this light-screening sheath was removed and laticifers exposed to light, rapid bleaching of the thiarubrine contents occurred. The leaves and stems of A. chamissonis seedlings were found to contain 10.5+/-6.8 microg/g total anthocyanins, predominantly cyanidin 3-O-(6'-O-malonylglucoside) and cyanidin 3-O-glucoside, while none was detected in roots. To correlate anthocyanin distribution with thiarubrine photoprotection, changes in thiarubrine A and thiophene A levels were measured in seedlings exposed to light. In roots, thiarubrine A levels decreased by 94% after 30 min of irradiation, and thiarubrines were completely absent after 4 h. A concomitant 3-fold increase in thiophene A levels in roots occurred during light exposure. In leaves and stems, thiarubrine A levels did not change appreciably during light exposure, with a nominal increase from 102.8+/-33.1 microg/g FW to 108.4+/-20.7 microg/g FW after 4 h. To confirm their photoprotective function, solutions of cyanidin 3-O-glucoside were used to filter visible light incident on a solution of thiarubrine A. Anthocyanin solutions of greater than 0.1 mM completely prevented thiarubrine photoconversion. This is the first report that anthocyanins function to photoprotect light-sensitive defensive chemicals in plants.

Alkynes↗
PubMed2006

Rapid colorimetric screening of drug interaction and penetration through lipid barriers.

PURPOSE: The aims of this study are to develop a rapid colorimetric assay for evaluating membrane interactions and penetration through lipid barriers and to create a platform, amenable to high-throughput screening formats, for predicting the extent of penetration of pharmaceutical compounds through lipid layers. METHODS: The colorimetric platform comprises vesicles of phospholipids and the chromatic lipid-mimetic polymer polydiacetylene. The polymer undergoes visible, concentration-dependent blue-red transformations induced through interactions of the vesicles with the molecules examined. RESULTS: We observe rapid colorimetric transitions induced by addition of pharmaceutical compounds to the chromatic vesicle solutions. We find that the concentration ranges for which the color transitions are induced in the lipid/polymer vesicles are correlated with the degree of lipid interactions and bilayer penetration of the tested compounds. The colorimetric platform could distinguish between three primary types of membrane-permeation profiles: bilayer-surface attachment, membrane penetration, and absence of lipid interactions. Application of complementary bioanalytical techniques corroborated the interpretation of the colorimetric data. Different pharmaceutical compounds were tested by the new assay. The results indicated clearly distinct membrane interaction profiles for molecules expected by conventional methods to have similar membrane-insertion properties (i.e., close log D/log P values). In addition, the new colorimetric assay pointed to similar membrane activities for molecules having highly divergent log Ds. CONCLUSIONS: The colorimetric assay facilitates "color coding" that could distinguish among different membrane permeation profiles. The data point to the usefulness of the platform for characterization of drug compound interactions with lipid assemblies. The new colorimetric technology constitutes a generic, extremely fast, and easily applicable approach for predicting and screening interactions of pharmaceutical compounds with lipid barriers.

Colorimetry↗