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R P Steer - One of the best experts on this subject based on the ideXlab platform.
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subpicosecond vibrational relaxation of the s1 states of azulene and Guaiazulene in solution
Canadian Journal of Chemistry, 1995Co-Authors: Dietrich Tittelbachhelmrich, Brian D Wagner, R P SteerAbstract:The S, population decay times of azulene and 1,4-dimethyl-7-isopropylazulene (Guaiazulene) in solution have been determined as a function of their initial vibrational energy content, EL,,, using a pump-probe experiment with subpicosecond time resolution. The S, lifetime of azulene does not depend on ELib for energies up to 1760 cm-I, whereas the lifetime of the shorter-lived S, state of Guaiazulene is independent of ELi, only for energies up to - 1000 cm-'. At higher energies, the lifetime decreases with increasing EL,,, and exhibits the same behavior in two structurally different solvents. It is suggested that internal conversion to the electronic ground state from a vibrationally unrelaxed S, state is responsible for the effects observed in Guaiazulene, and that intramolecular vibrational redistribution occurs with a time constant of several hundred femtoseconds.
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Subpicosecond vibrational relaxation of the S1 states of azulene and Guaiazulene in solution
Canadian Journal of Chemistry, 1995Co-Authors: Dietrich Tittelbach-helmrich, Brian D Wagner, R P SteerAbstract:The S1 population decay times of azulene and 1,4-dimethyl-7-isopropylazulene (Guaiazulene) in solution have been determined as a function of their initial vibrational energy content, [Formula: see text] using a pump–probe experiment with subpicosecond time resolution. The S1 lifetime of azulene does not depend on [Formula: see text] for energies up to 1760 cm−1, whereas the lifetime of the shorter-lived S1 state of Guaiazulene is independent of [Formula: see text] only for energies up to ~1000 cm−1. At higher energies, the lifetime decreases with increasing [Formula: see text] and exhibits the same behavior in two structurally different solvents. It is suggested that internal conversion to the electronic ground state from a vibrationally unrelaxed S1 state is responsible for the effects observed in Guaiazulene, and that intramolecular vibrational redistribution occurs with a time constant of several hundred femtoseconds. Keywords: pump–probe spectroscopy, azulene, femtosecond processes.
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Radiationless decay of the S2 states of azulene and related compounds: solvent dependence and the energy gap law
The Journal of Physical Chemistry, 1992Co-Authors: Brian D Wagner, Dietrich Tittelbach-helmrich, R P SteerAbstract:The UV-visible absorption spectra, S 2 lifetimes, and S 2 S 0 fluorescence quantum yields of azulene, azulene-d 8 , 1,3-di-chloroazulene, 1,3-dibromoazulene, 4,6,8-trimethylazulene, and 1,4-dimethyl-7-isopropylazulene (Guaiazulene) have each been measured accurately in six solvents. The S 2 -S 1 electronic energy spacing of each solute vary by ca. 500 cm -1 in thesesolvents
Brian D Wagner - One of the best experts on this subject based on the ideXlab platform.
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subpicosecond vibrational relaxation of the s1 states of azulene and Guaiazulene in solution
Canadian Journal of Chemistry, 1995Co-Authors: Dietrich Tittelbachhelmrich, Brian D Wagner, R P SteerAbstract:The S, population decay times of azulene and 1,4-dimethyl-7-isopropylazulene (Guaiazulene) in solution have been determined as a function of their initial vibrational energy content, EL,,, using a pump-probe experiment with subpicosecond time resolution. The S, lifetime of azulene does not depend on ELib for energies up to 1760 cm-I, whereas the lifetime of the shorter-lived S, state of Guaiazulene is independent of ELi, only for energies up to - 1000 cm-'. At higher energies, the lifetime decreases with increasing EL,,, and exhibits the same behavior in two structurally different solvents. It is suggested that internal conversion to the electronic ground state from a vibrationally unrelaxed S, state is responsible for the effects observed in Guaiazulene, and that intramolecular vibrational redistribution occurs with a time constant of several hundred femtoseconds.
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Subpicosecond vibrational relaxation of the S1 states of azulene and Guaiazulene in solution
Canadian Journal of Chemistry, 1995Co-Authors: Dietrich Tittelbach-helmrich, Brian D Wagner, R P SteerAbstract:The S1 population decay times of azulene and 1,4-dimethyl-7-isopropylazulene (Guaiazulene) in solution have been determined as a function of their initial vibrational energy content, [Formula: see text] using a pump–probe experiment with subpicosecond time resolution. The S1 lifetime of azulene does not depend on [Formula: see text] for energies up to 1760 cm−1, whereas the lifetime of the shorter-lived S1 state of Guaiazulene is independent of [Formula: see text] only for energies up to ~1000 cm−1. At higher energies, the lifetime decreases with increasing [Formula: see text] and exhibits the same behavior in two structurally different solvents. It is suggested that internal conversion to the electronic ground state from a vibrationally unrelaxed S1 state is responsible for the effects observed in Guaiazulene, and that intramolecular vibrational redistribution occurs with a time constant of several hundred femtoseconds. Keywords: pump–probe spectroscopy, azulene, femtosecond processes.
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Radiationless decay of the S2 states of azulene and related compounds: solvent dependence and the energy gap law
The Journal of Physical Chemistry, 1992Co-Authors: Brian D Wagner, Dietrich Tittelbach-helmrich, R P SteerAbstract:The UV-visible absorption spectra, S 2 lifetimes, and S 2 S 0 fluorescence quantum yields of azulene, azulene-d 8 , 1,3-di-chloroazulene, 1,3-dibromoazulene, 4,6,8-trimethylazulene, and 1,4-dimethyl-7-isopropylazulene (Guaiazulene) have each been measured accurately in six solvents. The S 2 -S 1 electronic energy spacing of each solute vary by ca. 500 cm -1 in thesesolvents
Sílvia M. Rocha - One of the best experts on this subject based on the ideXlab platform.
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Assessment of the antioxidant and antiproliferative effects of sesquiterpenic compounds in in vitro Caco-2 cell models
Food chemistry, 2014Co-Authors: Juliana Vinholes, Pedro Gonçalves, Fátima Martel, Manuel A. Coimbra, Sílvia M. RochaAbstract:In this study, the antiradical and antiproliferative effects of the sesquiterpenic compounds trans, trans-farnesol, cis-nerolidol, α-humulene and Guaiazulene, commonly found in plants and plant-derived foods and beverages, were evaluated. Chemical (DPPH and hydroxyl radicals) and biological (Caco-2 cells) models were used. Guaiazulene (IC50=0.73mM) showed higher scavenger capacity against DPPH, while trans, trans-farnesol (IC50=1.81mM) and cis-nerolidol (IC50=1.48mM) were more active towards hydroxyl radicals. All compounds, with the exception of α-humulene, were able to protect Caco-2 cells from oxidative stress induced by tert-butyl hydroperoxide. As antiproliferative agents, Guaiazulene and cis-nerolidol were more effective than trans, trans-farnesol and α-humulene. The results obtained for the sesquiterpenic compounds by these in vitro assays opens a perspective for their promising use as antioxidants and antiproliferative agents. However, in vivo tests should be carried out in the future to confirm their safety and effectiveness.
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Enhancement of Escherichia coli and Staphylococcus aureus antibiotic susceptibility using sesquiterpenoids.
Medicinal chemistry (Shariqah (United Arab Emirates)), 2008Co-Authors: Manuel Simões, Manuel A. Coimbra, Sílvia M. Rocha, Maria João VieiraAbstract:The present work examines the potential of sesquiterpenoids to sensitize Escherichia coli and Staphylococcus aureus, and modulate their susceptibility to the standard antibiotics ciprofloxacin, erythromycin, gentamicin and vancomycin. It was tested samples of three sesquiterpenoids: Guaiazulene, nerolidol (racemic mixture of the cis and trans isomers) and germacrene D enriched natural extract. Experiments were conducted aiming to assess the antimicrobial effects of the antibiotic-sesquiterpenoid combination on bacterial growth inhibition, by the disc diffusion assay and the minimum inhibitory concentration (MIC) assessment, the bactericidal effects, the post-antibiotic effect (PAE) and the effect on membrane permeability. The data related with the antimicrobial activity evidenced, through the disc diffusion assay, an antibiotic S. aureus antimicrobial activity enhancement by sesquiterpenoids presence. The MIC value for E. coli decreased significantly by sesquiterpenoids combination with ciprofloxacin, erythromycin and gentamicin, and for S. aureus, with all four selected antibiotics. This combination also increased the PAE, with the exception of Guaiazulene, which seemed to quench antibiotic antimicrobial action. A moderate correlation between antimicrobial action and impairment of cell membrane function was detected for germacrene D enriched extract, and nerolidol, as single treatments and in combination with antibiotic, while a poor correlation was obtained for Guaiazulene. This study provides basis for the evaluation of sesquiterpenoids as alternative or possible synergistic compounds for current antimicrobial chemotherapeutics, showing the practical utility of natural derived products to increase the susceptibility of E. coli and S. aureus.
Dietrich Tittelbach-helmrich - One of the best experts on this subject based on the ideXlab platform.
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Subpicosecond vibrational relaxation of the S1 states of azulene and Guaiazulene in solution
Canadian Journal of Chemistry, 1995Co-Authors: Dietrich Tittelbach-helmrich, Brian D Wagner, R P SteerAbstract:The S1 population decay times of azulene and 1,4-dimethyl-7-isopropylazulene (Guaiazulene) in solution have been determined as a function of their initial vibrational energy content, [Formula: see text] using a pump–probe experiment with subpicosecond time resolution. The S1 lifetime of azulene does not depend on [Formula: see text] for energies up to 1760 cm−1, whereas the lifetime of the shorter-lived S1 state of Guaiazulene is independent of [Formula: see text] only for energies up to ~1000 cm−1. At higher energies, the lifetime decreases with increasing [Formula: see text] and exhibits the same behavior in two structurally different solvents. It is suggested that internal conversion to the electronic ground state from a vibrationally unrelaxed S1 state is responsible for the effects observed in Guaiazulene, and that intramolecular vibrational redistribution occurs with a time constant of several hundred femtoseconds. Keywords: pump–probe spectroscopy, azulene, femtosecond processes.
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Radiationless decay of the S2 states of azulene and related compounds: solvent dependence and the energy gap law
The Journal of Physical Chemistry, 1992Co-Authors: Brian D Wagner, Dietrich Tittelbach-helmrich, R P SteerAbstract:The UV-visible absorption spectra, S 2 lifetimes, and S 2 S 0 fluorescence quantum yields of azulene, azulene-d 8 , 1,3-di-chloroazulene, 1,3-dibromoazulene, 4,6,8-trimethylazulene, and 1,4-dimethyl-7-isopropylazulene (Guaiazulene) have each been measured accurately in six solvents. The S 2 -S 1 electronic energy spacing of each solute vary by ca. 500 cm -1 in thesesolvents
Shin-ichi Takekuma - One of the best experts on this subject based on the ideXlab platform.
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Preparation, Structures, and Properties of New Monocarbenium Ion Compounds Stabilized by a 3-Guaiazulenyl Group and an Azobenzene Unit : Comparative Studies on Three Delocalized π-Electron Systems
Bulletin of the Chemical Society of Japan, 2009Co-Authors: Shin-ichi Takekuma, Toshie Minematsu, Kenji Fukuda, Yasuko Kawase, Hideko TakekumaAbstract:Reaction of Guaiazulene (=7-isopropyl-1,4-dimethylazulene) with 4′-hydroxyazobenzene-4-carbaldehyde in methanol in the presence of hexafluorophosphoric acid at 25 °C for 2 h gives as high as 94% yi...
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An efficient preparation, crystal structures, and properties of monocarbenium-ion compounds stabilized by 3-guaiazulenyl and anisyl groups
Tetrahedron, 2007Co-Authors: Shin-ichi Takekuma, Toshie Minematsu, Masayuki Tamura, Hideko TakekumaAbstract:Abstract Reaction of Guaiazulene (1) with 2-methoxybenzaldehyde (2) in methanol in the presence of hexafluorophosphoric acid at 25 °C for 2 h gives (3-guaiazulenyl)(2-methoxyphenyl)methylium hexafluorophosphate (5a) in 93% yield. Similarly, reaction of 1 with 3-methoxybenzaldehyde (3) or 4-methoxybenzaldehyde (4) under the same reaction conditions as for 2 affords (3-guaiazulenyl)(3-methoxyphenyl)methylium hexafluorophosphate (6) (91% yield) or (3-guaiazulenyl)(4-methoxyphenyl)methylium hexafluorophosphate (7) (97% yield). The crystal structures as well as the spectroscopic, electrochemical, and chemical properties of these monocarbenium-ion compounds, possessing interesting resonance forms, stabilized by the 3-guaiazulenyl and anisyl (i.e., 2-, 3-, or 4-methoxyphenyl) groups are reported.
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The Facile Preparation, Crystal Structure, and Chemical and Electrochemical Properties of 9-Anthryl-3-guaiazulenylmethylium Hexafluorophosphate
Bulletin of the Chemical Society of Japan, 2004Co-Authors: Shin-ichi Takekuma, Kaori Sasaki, Miwa Nakatsuji, Masato Sasaki, Toshie Minematsu, Hideko TakekumaAbstract:Reaction of Guaiazulene (1) with anthracene-9-carbaldehyde in methanol in the presence of hexafluorophosphoric acid at 25 °C for 30 min gave the title compound 2 in 88% yield.
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A facile preparation, the crystal structure, the chemical and electrochemical properties of [4-(dimethylamino)phenyl]-3-guaiazulenylmethylium tetrafluoroborate
Tetrahedron, 2003Co-Authors: Masato Sasaki, Toshie Minematsu, Hideko Takekuma, Masaru Nakamura, Takayuki Uriu, Masakuni Yoshihara, Shin-ichi TakekumaAbstract:Reaction of Guaiazulene (1) with p-dimethylaminobenzaldehyde in methanol in the presence of tetrafluoroboric acid gives the title monocarbocation compound, [4-(dimethylamino)phenyl]-3-guaiazulenylmethylium tetrafluoroborate (2), in 90% yield. The title investigations of compound 2 compared with those of two other monocarbocations stabilized by a 3-guaiazulenyl group (i.e. phenyl-3-guaiazulenylmethyl and [4-(isopropyl)phenyl]-3-guaiazulenylmethyl cations) are reported.
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An efficient preparation, the structure and the properties of 1-isopropyl-4-(3-guaiazulenylmethylium)benzene hexafluorophosphate and tetrafluoroborate
Tetrahedron Letters, 2002Co-Authors: Shin-ichi Takekuma, Masato Sasaki, Mariko Tanizawa, Takuya Matsumoto, Hideko TakekumaAbstract:Abstract Reactions of Guaiazulene ( 1 ) with 4-isopropylbenzaldehyde in acetic acid in the presence of hexafluorophosphoric acid (and tetrafluoroboronic acid) at 25°C for 2 h under aerobic conditions quantitatively give the new title monocarbocation compounds, 1-isopropyl-4-(3-guaiazulenylmethylium)benzene hexafluorophosphate ( 4 ) and the tetrafluoroborate ( 5 ), which upon reaction with sodium methoxide dissolved in methanol in acetonitrile at 0°C for 20 min, respectively, afford as high as 92% isolated yield of 1-isopropyl-4-(3-guaiazulenylmethoxymethyl)benzene ( 8 ). The crystal structure of 5 , as the first example of carbocations stabilized by azulenyl groups, and the characteristic and chemical properties of 4 and 5 are reported.
