The Experts below are selected from a list of 17364 Experts worldwide ranked by ideXlab platform
Mun Yhung Jung - One of the best experts on this subject based on the ideXlab platform.
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electron spin resonance and luminescence spectroscopic observation and kinetic study of Chemical and physical singlet oxygen Quenching by resveratrol in methanol
2010Co-Authors: Mun Yhung Jung, Dong Seong ChoiAbstract:Electron spin resonance (ESR) spectroscopy and near-infrared (NIR) fluorescence spectroscopy were performed to observe singlet oxygen Quenching by resveratrol. Resveratrol greatly decreased the 2,2,6,6-Tetramethyl-4-piperidone-N-oxyl radical signal as determined by ESR spectroscopy. Resveratrol also efficiently decreased luminescence emission at 1268 nm as studied with a NIR spectrofluorometer, showing positive evidence of singlet oxygen Quenching by resveratrol. The total singlet oxygen Quenching rate constant (kr + kq) of resveratrol in methanol was determined to be 2.55 × 107 M−1 s−1. The singlet oxygen Chemical Quenching rate constant (kr) of resveratrol was calculated by measuring its reaction rate with singlet oxygen relative to that of α-terpinene in the same solution under light illumination. The kr value of resveratrol was 1.15 × 106 M−1 s−1. The percent partition of Chemical Quenching over total singlet oxygen Quenching (kr × 100)/(kr + kq) for resveratrol was 5.11%. The results showed that resv...
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Direct Spectroscopic Observation of Singlet Oxygen Quenching and Kinetic Studies of Physical and Chemical Singlet Oxygen Quenching Rate Constants of Synthetic Antioxidants (BHA, BHT, and TBHQ) in Methanol
2010Co-Authors: Jun Hyun Lee, Mun Yhung JungAbstract:Singlet oxygen Quenching by synthetic antioxidants (BHA, BHT, and TBHQ) was directly observed by spectroscopic monitoring of luminescence at 1268 nm. The luminescence data showed unambiguous evidence of singlet oxygen Quenching by synthetic phenolic antioxidants with the highest activity for TBHQ, followed by BHA and BHT. The protective activities of these synthetic antioxidants on alpha-terpinene oxidation with Chemically-induced singlet oxygen under dark further confirmed their singlet oxygen Quenching abilities. Total singlet oxygen Quenching rate constants (k(r) + k(q)) of BHA, BHT, and TBHQ were determined in a system containing alpha-terpinene (as a singlet oxygen trap) and methylene blue (as a sensitizer) during light irradiation, and the values were 5.14 x 10(7), 3.41 x 10(6), and 1.99 x 10(8) M(-1)s(-1), respectively. After the k(r) value of alpha-terpinene was first determined, the k(r) values of the synthetic antioxidants were calculated by measuring their relative reaction rates with singlet oxygen to that of alpha-terpinene under the identical conditions. The k(r) values of the BHA, BHT, and TBHQ were 3.90 x 10(5), 1.23 x 10(5), and 2.93 x 10(6), M(-1)s(-1). The percent partition of Chemical Quenching over total singlet oxygen Quenching (k(r) x 100)/(k(r) + k(q)) for BHA, BHT, and TBHQ were 0.76%, 3.61%, and 1.47%, respectively. The results showed that the synthetic antioxidants quench singlet oxygen almost exclusively through the mechanism of physical Quenching. This represents the first report on the singlet oxygen Quenching mechanism of these synthetic antioxidants. Practical Application: The synthetic antioxidants, especially TBHQ, have been found to have a strong singlet oxygen Quenching ability. This article also clearly showed that singlet oxygen Quenching by synthetic antioxidants was mainly by the physical Quenching mechanism. The results suggested that these synthetic antioxidants, especially TBHQ, could be used practically for the protection of the food components such as edible oils and vitamins against singlet oxygen induced oxidations without significant losses of antioxidant activity during storage under light.
R Lupu - One of the best experts on this subject based on the ideXlab platform.
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the effect of disequilibrium carbon chemistry on the atmospheric circulation and phase curves of hot jupiter hd 189733b
2018Co-Authors: Maria E Steinrueck, Vivien Parmentier, Adam P Showman, Joshua D Lothringer, R LupuAbstract:On hot Jupiter exoplanets, strong horizontal and vertical winds should homogenize the abundances of the important absorbers CH$_4$ and CO much faster than Chemical reactions restore Chemical equilibrium. This effect, typically neglected in general circulation models (GCMs), has been suggested as explanation for discrepancies between observed infrared lightcurves and those predicted by GCMs: On the nightsides of several hot Jupiters, GCMs predict outgoing fluxes that are too large, especially in the Spitzer 4.5 $\mu$m band. We modified the SPARC/MITgcm to include disequilibrium abundances of CH$_4$, CO and H$_2$O by assuming that the CH$_4$/CO ratio is constant throughout the simulation domain. We ran simulations of hot Jupiter HD 189733b with 8 CH$_4$/CO ratios. In the more likely CO-dominated regime, we find temperature changes of $\sim$50 K compared to the equilibrium chemistry case across large regions. This effect is large enough to affect predicted emission spectra and should thus be included in GCMs of hot Jupiters with equilibrium temperatures below 1300 K. We find that spectra in regions with strong methane absorption, including the Spitzer 3.6 and 8 $\mu$m bands, are strongly impacted by disequilibrium abundances. We expect Chemical Quenching to result in much larger nightside fluxes in the 3.6 $\mu$m band, in stark contrast to observations. Meanwhile, we find almost no effect on predicted observations in the 4.5 $\mu$m band, as the opacity changes due to CO and H$_2$O offset each other. We thus conclude that disequilibrium carbon chemistry cannot explain the observed low nightside fluxes in the 4.5 $\mu$m band.
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the effect of 3d transport induced disequilibrium carbon chemistry on the atmospheric structure and phase curves and emission spectra of hot jupiter hd 189733b
2018Co-Authors: Maria E Steinrueck, Vivien Parmentier, Adam P Showman, Joshua D Lothringer, R LupuAbstract:On hot Jupiter exoplanets, strong horizontal and vertical winds should homogenize the abundances of the important absorbers CH$_4$ and CO much faster than Chemical reactions restore Chemical equilibrium. This effect, typically neglected in general circulation models (GCMs), has been suggested as explanation for discrepancies between observed infrared lightcurves and those predicted by GCMs: On the nightsides of several hot Jupiters, GCMs predict outgoing fluxes that are too large, especially in the Spitzer 4.5 $\mu$m band. We modified the SPARC/MITgcm to include disequilibrium abundances of CH$_4$, CO and H$_2$O by assuming that the CH$_4$/CO ratio is constant throughout the simulation domain. We ran simulations of hot Jupiter HD 189733b with 8 CH$_4$/CO ratios. In the more likely CO-dominated regime, we find temperature changes $\geq$50-100 K compared to the equilibrium chemistry case across large regions. This effect is large enough to affect predicted emission spectra and should thus be included in GCMs of hot Jupiters with equilibrium temperatures between 600K and 1300K. We find that spectra in regions with strong methane absorption, including the Spitzer 3.6 and 8 $\mu$m bands, are strongly impacted by disequilibrium abundances. We expect Chemical Quenching to result in much larger nightside fluxes in the 3.6 $\mu$m band, in stark contrast to observations. Meanwhile, we find almost no effect on predicted observations in the 4.5 $\mu$m band, as the opacity changes due to CO and H$_2$O offset each other. We thus conclude that disequilibrium carbon chemistry cannot explain the observed low nightside fluxes in the 4.5 $\mu$m band.
M Bilska - One of the best experts on this subject based on the ideXlab platform.
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interaction of singlet molecular oxygen with melatonin and related indoles
2003Co-Authors: Zenon Matuszak, M Bilska, Krzysztof J ReszkaAbstract:Abstract Singlet molecular oxygen (1O2) is one of the major agents responsible for (photo)oxidative damage in biological systems including human skin and eyes. It has been reported that the neural hormone melatonin (MLT) can abrogate 1O2-mediated cytotoxicity through its purported high antioxidant activity. We studied the interaction of MLT with 1O2 in deuterium oxide (D2O), acetonitrile and methanol by measuring the phosphorescence lifetime of 1O2 in the presence of MLT and related indoles for comparison. Rose bengal (RB) was used as the main 1O2 photosensitizer. The rate constant (kq) for the total (physical and Chemical) Quenching of 1O2 by MLT was determined to be 4.0 × 107 M–1 s–1 in D2O (pD 7), 6.0 × 107 M–1 s–1 in acetonitrile, and 6.1 × 107 M–1 s–1 in methanol-d1. The related indoles, tryptophan, 5-hydroxyindole, 5-methoxytryptamine, 5-hydroxytryptamine (5-OH-T, serotonin), 6-hydroxymelatonin (6-OH-MLT) and 6-chloromelatonin quenched 1O2 phosphorescence with similar kq values. We also compared the...
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interaction of singlet molecular oxygen with double fluorescent and spin sensors
2003Co-Authors: Kalman Hideg, Tamas Kalai, M BilskaAbstract:Abstract Double fluorescent and spin sensors were recently used to detect transient oxidants via simultaneous fluorescence change and production of the nitroxide radical detected by electron paramagnetic resonance. One such oxidant, singlet molecular oxygen ( 1 O 2 ), was detected in thylakoid membrane using these probes. In the present study, we investigated the total (physical and Chemical) Quenching of 1 O 2 phosphorescence by sensors composed of the 2,5-dihydro-2,2,5,5-tetramethyl-1 H -pyrrole moiety attached to xanthene or dansyl fluorophores. We found that the Quenching rate constants were in the range (2–7) × 10 7 M −1 s −1 in acetonitrile and D 2 O. Quenching of 1 O 2 is usually an additive process in which different functional groups may contribute. We estimated that the 1 O 2 Quenching by the amine fragments was ca. one to two orders of magnitude lower than that for the complete molecules. Our data suggest that the incorporation of a fluorescent chromophore results in additional strong Quenching of 1 O 2 , which may in turn decrease the nitroxide yield via the 1 O 2 Chemical path, possibly having an effect on quantitative interpretations. We have also found that probes with the dansyl fluorophore photosensitized 1 O 2 upon UV excitation with the quantum yield of 0.087 in acetonitrile at 366 nm. This result shows that care must be taken when the dansyl-based sensors are used in experiments requiring UV irradiation. We hope that our results will contribute to a better characterization and wider use of these novel double sensors.
Vivien Parmentier - One of the best experts on this subject based on the ideXlab platform.
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global chemistry and thermal structure models for the hot jupiter wasp 43b and predictions for jwst
2020Co-Authors: Olivia Venot, Vivien Parmentier, Jasmina Blecic, Patricio E Cubillos, Ingo Waldmann, Quentin Changeat, Julianne I Moses, P Tremblin, Nicolas Crouzet, Peter GaoAbstract:The James Webb Space Telescope (JWST) is expected to revolutionize the field of exoplanets. The broad wavelength coverage and the high sensitivity of its instruments will allow characterization of exoplanetary atmospheres with unprecedented precision. Following the Call for the Cycle 1 Early Release Science Program, the Transiting Exoplanet Community was awarded time to observe several targets, including WASP-43b. The atmosphere of this hot Jupiter has been intensively observed but still harbors some mysteries, especially concerning the day-night temperature gradient, the efficiency of the atmospheric circulation, and the presence of nightside clouds. We will constrain these properties by observing a full orbit of the planet and extracting its spectroscopic phase curve in the 5--12 $\mu$m range with JWST/MIRI. To prepare for these observations, we performed an extensive modeling work with various codes: radiative transfer, Chemical kinetics, cloud microphysics, global circulation models, JWST simulators, and spectral retrieval. Our JWST simulations show that we should achieve a precision of 210 ppm per 0.1 $\mu$m spectral bin on average, which will allow us to measure the variations of the spectrum in longitude and measure the night-side emission spectrum for the first time. If the atmosphere of WASP-43b is clear, our observations will permit us to determine if its atmosphere has an equilibrium or disequilibrium Chemical composition, providing eventually the first conclusive evidence of Chemical Quenching in a hot Jupiter atmosphere. If the atmosphere is cloudy, a careful retrieval analysis will allow us to identify the cloud composition.
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the effect of disequilibrium carbon chemistry on the atmospheric circulation and phase curves of hot jupiter hd 189733b
2018Co-Authors: Maria E Steinrueck, Vivien Parmentier, Adam P Showman, Joshua D Lothringer, R LupuAbstract:On hot Jupiter exoplanets, strong horizontal and vertical winds should homogenize the abundances of the important absorbers CH$_4$ and CO much faster than Chemical reactions restore Chemical equilibrium. This effect, typically neglected in general circulation models (GCMs), has been suggested as explanation for discrepancies between observed infrared lightcurves and those predicted by GCMs: On the nightsides of several hot Jupiters, GCMs predict outgoing fluxes that are too large, especially in the Spitzer 4.5 $\mu$m band. We modified the SPARC/MITgcm to include disequilibrium abundances of CH$_4$, CO and H$_2$O by assuming that the CH$_4$/CO ratio is constant throughout the simulation domain. We ran simulations of hot Jupiter HD 189733b with 8 CH$_4$/CO ratios. In the more likely CO-dominated regime, we find temperature changes of $\sim$50 K compared to the equilibrium chemistry case across large regions. This effect is large enough to affect predicted emission spectra and should thus be included in GCMs of hot Jupiters with equilibrium temperatures below 1300 K. We find that spectra in regions with strong methane absorption, including the Spitzer 3.6 and 8 $\mu$m bands, are strongly impacted by disequilibrium abundances. We expect Chemical Quenching to result in much larger nightside fluxes in the 3.6 $\mu$m band, in stark contrast to observations. Meanwhile, we find almost no effect on predicted observations in the 4.5 $\mu$m band, as the opacity changes due to CO and H$_2$O offset each other. We thus conclude that disequilibrium carbon chemistry cannot explain the observed low nightside fluxes in the 4.5 $\mu$m band.
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the effect of 3d transport induced disequilibrium carbon chemistry on the atmospheric structure and phase curves and emission spectra of hot jupiter hd 189733b
2018Co-Authors: Maria E Steinrueck, Vivien Parmentier, Adam P Showman, Joshua D Lothringer, R LupuAbstract:On hot Jupiter exoplanets, strong horizontal and vertical winds should homogenize the abundances of the important absorbers CH$_4$ and CO much faster than Chemical reactions restore Chemical equilibrium. This effect, typically neglected in general circulation models (GCMs), has been suggested as explanation for discrepancies between observed infrared lightcurves and those predicted by GCMs: On the nightsides of several hot Jupiters, GCMs predict outgoing fluxes that are too large, especially in the Spitzer 4.5 $\mu$m band. We modified the SPARC/MITgcm to include disequilibrium abundances of CH$_4$, CO and H$_2$O by assuming that the CH$_4$/CO ratio is constant throughout the simulation domain. We ran simulations of hot Jupiter HD 189733b with 8 CH$_4$/CO ratios. In the more likely CO-dominated regime, we find temperature changes $\geq$50-100 K compared to the equilibrium chemistry case across large regions. This effect is large enough to affect predicted emission spectra and should thus be included in GCMs of hot Jupiters with equilibrium temperatures between 600K and 1300K. We find that spectra in regions with strong methane absorption, including the Spitzer 3.6 and 8 $\mu$m bands, are strongly impacted by disequilibrium abundances. We expect Chemical Quenching to result in much larger nightside fluxes in the 3.6 $\mu$m band, in stark contrast to observations. Meanwhile, we find almost no effect on predicted observations in the 4.5 $\mu$m band, as the opacity changes due to CO and H$_2$O offset each other. We thus conclude that disequilibrium carbon chemistry cannot explain the observed low nightside fluxes in the 4.5 $\mu$m band.
Maria E Steinrueck - One of the best experts on this subject based on the ideXlab platform.
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the effect of disequilibrium carbon chemistry on the atmospheric circulation and phase curves of hot jupiter hd 189733b
2018Co-Authors: Maria E Steinrueck, Vivien Parmentier, Adam P Showman, Joshua D Lothringer, R LupuAbstract:On hot Jupiter exoplanets, strong horizontal and vertical winds should homogenize the abundances of the important absorbers CH$_4$ and CO much faster than Chemical reactions restore Chemical equilibrium. This effect, typically neglected in general circulation models (GCMs), has been suggested as explanation for discrepancies between observed infrared lightcurves and those predicted by GCMs: On the nightsides of several hot Jupiters, GCMs predict outgoing fluxes that are too large, especially in the Spitzer 4.5 $\mu$m band. We modified the SPARC/MITgcm to include disequilibrium abundances of CH$_4$, CO and H$_2$O by assuming that the CH$_4$/CO ratio is constant throughout the simulation domain. We ran simulations of hot Jupiter HD 189733b with 8 CH$_4$/CO ratios. In the more likely CO-dominated regime, we find temperature changes of $\sim$50 K compared to the equilibrium chemistry case across large regions. This effect is large enough to affect predicted emission spectra and should thus be included in GCMs of hot Jupiters with equilibrium temperatures below 1300 K. We find that spectra in regions with strong methane absorption, including the Spitzer 3.6 and 8 $\mu$m bands, are strongly impacted by disequilibrium abundances. We expect Chemical Quenching to result in much larger nightside fluxes in the 3.6 $\mu$m band, in stark contrast to observations. Meanwhile, we find almost no effect on predicted observations in the 4.5 $\mu$m band, as the opacity changes due to CO and H$_2$O offset each other. We thus conclude that disequilibrium carbon chemistry cannot explain the observed low nightside fluxes in the 4.5 $\mu$m band.
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the effect of 3d transport induced disequilibrium carbon chemistry on the atmospheric structure and phase curves and emission spectra of hot jupiter hd 189733b
2018Co-Authors: Maria E Steinrueck, Vivien Parmentier, Adam P Showman, Joshua D Lothringer, R LupuAbstract:On hot Jupiter exoplanets, strong horizontal and vertical winds should homogenize the abundances of the important absorbers CH$_4$ and CO much faster than Chemical reactions restore Chemical equilibrium. This effect, typically neglected in general circulation models (GCMs), has been suggested as explanation for discrepancies between observed infrared lightcurves and those predicted by GCMs: On the nightsides of several hot Jupiters, GCMs predict outgoing fluxes that are too large, especially in the Spitzer 4.5 $\mu$m band. We modified the SPARC/MITgcm to include disequilibrium abundances of CH$_4$, CO and H$_2$O by assuming that the CH$_4$/CO ratio is constant throughout the simulation domain. We ran simulations of hot Jupiter HD 189733b with 8 CH$_4$/CO ratios. In the more likely CO-dominated regime, we find temperature changes $\geq$50-100 K compared to the equilibrium chemistry case across large regions. This effect is large enough to affect predicted emission spectra and should thus be included in GCMs of hot Jupiters with equilibrium temperatures between 600K and 1300K. We find that spectra in regions with strong methane absorption, including the Spitzer 3.6 and 8 $\mu$m bands, are strongly impacted by disequilibrium abundances. We expect Chemical Quenching to result in much larger nightside fluxes in the 3.6 $\mu$m band, in stark contrast to observations. Meanwhile, we find almost no effect on predicted observations in the 4.5 $\mu$m band, as the opacity changes due to CO and H$_2$O offset each other. We thus conclude that disequilibrium carbon chemistry cannot explain the observed low nightside fluxes in the 4.5 $\mu$m band.