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Susan Collins - One of the best experts on this subject based on the ideXlab platform.

  • the luminescence spectra of the 8 methoxypsoralen excited state complexes and Photochemical Product in argon methanol argon and water argon matrices at 10 k
    Journal of Physical Chemistry A, 2000
    Co-Authors: Joseph Brownfield, Susan Collins
    Abstract:

    The luminescence spectra of the 8-methoxypsoralen, 8-MOP, excited-state complex have been observed in argon matrices at 10 K. The excited-state complex is most probably an excimer, formed for cases in which high concentrations of 8-MOP are deposited in a pure-argon matrix. For cases in which 8-MOP is in the presence of alcohol or water, another excited-state complex, an exciplex, is formed. Finally, when the 8-MOP/methanol/argon or 8-MOP/water/argon mixtures are photolyzed, a unique Photochemical Product is observed. This Product is most probably the ground-state dimer, similar to the coumarin dimer formed in alcohol solutions upon UV irradiation. The luminescence emission spectra of all three of the complexes are different and overlapping, resulting in spectra that seem anomalous. These results are similar to the reported anomalous emission spectrum of coumarin by Song, et al., which is chemically and spectroscopically similar to 8-MOP.1,2,3

  • The Luminescence Spectra of the 8-Methoxypsoralen Excited-State Complexes and Photochemical Product in Argon, Methanol/Argon, and Water/Argon Matrices at 10 K†
    The Journal of Physical Chemistry A, 2000
    Co-Authors: Joseph Brownfield, Susan Collins
    Abstract:

    The luminescence spectra of the 8-methoxypsoralen, 8-MOP, excited-state complex have been observed in argon matrices at 10 K. The excited-state complex is most probably an excimer, formed for cases in which high concentrations of 8-MOP are deposited in a pure-argon matrix. For cases in which 8-MOP is in the presence of alcohol or water, another excited-state complex, an exciplex, is formed. Finally, when the 8-MOP/methanol/argon or 8-MOP/water/argon mixtures are photolyzed, a unique Photochemical Product is observed. This Product is most probably the ground-state dimer, similar to the coumarin dimer formed in alcohol solutions upon UV irradiation. The luminescence emission spectra of all three of the complexes are different and overlapping, resulting in spectra that seem anomalous. These results are similar to the reported anomalous emission spectrum of coumarin by Song, et al., which is chemically and spectroscopically similar to 8-MOP.1,2,3

Joseph Brownfield - One of the best experts on this subject based on the ideXlab platform.

  • the luminescence spectra of the 8 methoxypsoralen excited state complexes and Photochemical Product in argon methanol argon and water argon matrices at 10 k
    Journal of Physical Chemistry A, 2000
    Co-Authors: Joseph Brownfield, Susan Collins
    Abstract:

    The luminescence spectra of the 8-methoxypsoralen, 8-MOP, excited-state complex have been observed in argon matrices at 10 K. The excited-state complex is most probably an excimer, formed for cases in which high concentrations of 8-MOP are deposited in a pure-argon matrix. For cases in which 8-MOP is in the presence of alcohol or water, another excited-state complex, an exciplex, is formed. Finally, when the 8-MOP/methanol/argon or 8-MOP/water/argon mixtures are photolyzed, a unique Photochemical Product is observed. This Product is most probably the ground-state dimer, similar to the coumarin dimer formed in alcohol solutions upon UV irradiation. The luminescence emission spectra of all three of the complexes are different and overlapping, resulting in spectra that seem anomalous. These results are similar to the reported anomalous emission spectrum of coumarin by Song, et al., which is chemically and spectroscopically similar to 8-MOP.1,2,3

  • The Luminescence Spectra of the 8-Methoxypsoralen Excited-State Complexes and Photochemical Product in Argon, Methanol/Argon, and Water/Argon Matrices at 10 K†
    The Journal of Physical Chemistry A, 2000
    Co-Authors: Joseph Brownfield, Susan Collins
    Abstract:

    The luminescence spectra of the 8-methoxypsoralen, 8-MOP, excited-state complex have been observed in argon matrices at 10 K. The excited-state complex is most probably an excimer, formed for cases in which high concentrations of 8-MOP are deposited in a pure-argon matrix. For cases in which 8-MOP is in the presence of alcohol or water, another excited-state complex, an exciplex, is formed. Finally, when the 8-MOP/methanol/argon or 8-MOP/water/argon mixtures are photolyzed, a unique Photochemical Product is observed. This Product is most probably the ground-state dimer, similar to the coumarin dimer formed in alcohol solutions upon UV irradiation. The luminescence emission spectra of all three of the complexes are different and overlapping, resulting in spectra that seem anomalous. These results are similar to the reported anomalous emission spectrum of coumarin by Song, et al., which is chemically and spectroscopically similar to 8-MOP.1,2,3

Thomas Kromer - One of the best experts on this subject based on the ideXlab platform.

  • Photodegradation and volatility of pesticides
    Environmental Science and Pollution Research, 2004
    Co-Authors: Thomas Kromer, Holger Ophoff, Andreas Stork, Fritz Führ
    Abstract:

    Background and Objectives Among the factors affecting the environmental fate of surface-applied pesticides several biological as well as abiotic factors, such as volatilization and Photochemical transformations are of particular interest. Whereas reliable measurement methods and models for estimating direct photodegradation are already available for the compartments of water and atmosphere and individual subprocesses have already been described in detail, there is still a need for further elucidation concerning the key processes of heterogeneous photodegradation of environmental chemicals on surfaces. Methods In order to systematically examine the direct and indirect photodegradation of^14C-labeled pesticides on various surfaces and their volatilization behavior, a new laboratory device (‘photovolatility chamber’) was designed according to US EPA Guideline §161-3. Model experiments under controlled conditions were conducted investigating the impact of different surfaces, i.e. glass, soil dust and radish plants, and environmental factors, i.e. irradiation and atmospheric ozone (O_3), on the photodegradation and volatilization of surface-deposited [phenyl-UL-^14C] parathion-methyl (PM). Results and Discussion Depending on the experimental conditions, parathion-methyl was converted to paraoxon-methyl, 4-nitrophenol, unknown polar Products and^14CO_2. With respect to the direct photodegradation of PM (experiments without O_3), the major Products were polar compounds and^14CO_2, due to the rapid Photochemical mineralization of 4-nitrophenol to^14CO_2. Paraoxon-methyl and 4-nitrophenol formation was mainly mediated by the combination of light, O_3, and -OH radicals. In radish experiments PM photodegradation was presumably located in the cuticle compartment, which exhibited a sensitized photodegradation, as more unknown Products were yielded compared to the glass and soil dust experiments. This could be explained by intensifying the inherent PM degradation in the dark with the same Product spectrum. Due to Photochemical Product formation, which is an antagonistic process to the volatilization of parent compound, the volatilization of unaltered parathion-methyl from each surface generally decreased in the presence of light, particularly in combination with increasing O_3 concentrations and OH radical Production rates. Conclusion First results demonstrated that the photovolatility chamber provides a special tool for the systematic evaluation of (a) photodegradation of surface-located pesticide residues, i.e. measuring qualitative aspects of direct and indirect photodegradation together with relative photodegradation rates, and (b) volatilization of pesticides on surfaces by including and optionally varying relevant parameters such as light, atmospheric O_3 concentration, surface temperature, air temperature, air flow rate. Outlook The experimental facility represents an important complement to lysimeter and field studies, in particular for experiments on the volatilization of pesticides using the wind tunnel system. With the photovolatiliry chamber special experiments on photodegradation, volatilization and plant uptake can be conducted to study key processes in more detail and this will lead to a better understanding of the effects of certain environmental processes on the fate of released agrochemicals contributing to an improved risk assessment.

  • Photodegradation and volatility of pesticides
    Environmental Science and Pollution Research, 2004
    Co-Authors: Thomas Kromer, Holger Ophoff, Andreas Stork, Fabiane Fuhr
    Abstract:

    Among the factors affecting the environmental fate of surface-applied pesticides several biological as well as abiotic factors, such as volatilization and Photochemical transformations are of particular interest. Whereas reliable measurement methods and models for estimating direct photodegradation are already available for the compartments of water and atmosphere and individual subprocesses have already been described in detail, there is still a need for further elucidation concerning the key processes of heterogeneous photodegradation of environmental chemicals on surfaces. In order to systematically examine the direct and indirect photodegradation of14C-labeled pesticides on various surfaces and their volatilization behavior, a new laboratory device (‘photovolatility chamber’) was designed according to US EPA Guideline §161-3. Model experiments under controlled conditions were conducted investigating the impact of different surfaces, i.e. glass, soil dust and radish plants, and environmental factors, i.e. irradiation and atmospheric ozone (O3), on the photodegradation and volatilization of surface-deposited [phenyl-UL-14C] parathion-methyl (PM). Depending on the experimental conditions, parathion-methyl was converted to paraoxon-methyl, 4-nitrophenol, unknown polar Products and14CO2. With respect to the direct photodegradation of PM (experiments without O3), the major Products were polar compounds and14CO2, due to the rapid Photochemical mineralization of 4-nitrophenol to14CO2. Paraoxon-methyl and 4-nitrophenol formation was mainly mediated by the combination of light, O3, and -OH radicals. In radish experiments PM photodegradation was presumably located in the cuticle compartment, which exhibited a sensitized photodegradation, as more unknown Products were yielded compared to the glass and soil dust experiments. This could be explained by intensifying the inherent PM degradation in the dark with the same Product spectrum. Due to Photochemical Product formation, which is an antagonistic process to the volatilization of parent compound, the volatilization of unaltered parathion-methyl from each surface generally decreased in the presence of light, particularly in combination with increasing O3 concentrations and OH radical Production rates. First results demonstrated that the photovolatility chamber provides a special tool for the systematic evaluation of (a) photodegradation of surface-located pesticide residues, i.e. measuring qualitative aspects of direct and indirect photodegradation together with relative photodegradation rates, and (b) volatilization of pesticides on surfaces by including and optionally varying relevant parameters such as light, atmospheric O3 concentration, surface temperature, air temperature, air flow rate. The experimental facility represents an important complement to lysimeter and field studies, in particular for experiments on the volatilization of pesticides using the wind tunnel system. With the photovolatiliry chamber special experiments on photodegradation, volatilization and plant uptake can be conducted to study key processes in more detail and this will lead to a better understanding of the effects of certain environmental processes on the fate of released agrochemicals contributing to an improved risk assessment.

Pallavi Sharma - One of the best experts on this subject based on the ideXlab platform.

  • Photochemical studies of the tridachiahydropyrones
    2010
    Co-Authors: Pallavi Sharma, John E. Moses
    Abstract:

    Sea water is a strong absorber of UV-B radiation. We hypothesized that the Photochemical Product distribution of a restricted family of marine-derived polypropionates may be affected by attenuation of UV in the natural habitat. Laboratory scale experiments support this hypothesis, indicating that dissolved organic materials (DOM) may play a decisive role in the distribution of photoProducts in marine animals lacking the protection of a shell.

  • Photochemical Studies of theTridachiahydropyrones in Seawater
    Synlett, 2009
    Co-Authors: Pallavi Sharma, John E. Moses
    Abstract:

    Sea water is a strong absorber of UV-B radiation. We hypothesized that the Photochemical Product distribution of a restricted family of marine-derived polypropionates may be affected by attenuation of UV in the natural habitat. Laboratory scale experiments support this hypothesis, indicating that dissolved organic materials (DOM) may play a decisive role in the distribution of photoProducts in marine animals lacking the protection of a shell.

  • Photochemical Studies of the Tridachiahydropyrones in Seawater
    Synlett, 2009
    Co-Authors: John Moses, Pallavi Sharma
    Abstract:

    Sea water is a strong absorber of UV-B radiation. We hypothesized that the Photochemical Product distribution of a restricted family of marine-derived polypropionates may be affected by attenuation of UV in the natural habitat. Laboratory scale experiments support this hypothesis, indicating that dissolved organic materials (DOM) may play a decisive role in the distribution of photoProducts in marine animals lacking the protection of a shell

Fabiane Fuhr - One of the best experts on this subject based on the ideXlab platform.

  • Photodegradation and volatility of pesticides
    Environmental Science and Pollution Research, 2004
    Co-Authors: Thomas Kromer, Holger Ophoff, Andreas Stork, Fabiane Fuhr
    Abstract:

    Among the factors affecting the environmental fate of surface-applied pesticides several biological as well as abiotic factors, such as volatilization and Photochemical transformations are of particular interest. Whereas reliable measurement methods and models for estimating direct photodegradation are already available for the compartments of water and atmosphere and individual subprocesses have already been described in detail, there is still a need for further elucidation concerning the key processes of heterogeneous photodegradation of environmental chemicals on surfaces. In order to systematically examine the direct and indirect photodegradation of14C-labeled pesticides on various surfaces and their volatilization behavior, a new laboratory device (‘photovolatility chamber’) was designed according to US EPA Guideline §161-3. Model experiments under controlled conditions were conducted investigating the impact of different surfaces, i.e. glass, soil dust and radish plants, and environmental factors, i.e. irradiation and atmospheric ozone (O3), on the photodegradation and volatilization of surface-deposited [phenyl-UL-14C] parathion-methyl (PM). Depending on the experimental conditions, parathion-methyl was converted to paraoxon-methyl, 4-nitrophenol, unknown polar Products and14CO2. With respect to the direct photodegradation of PM (experiments without O3), the major Products were polar compounds and14CO2, due to the rapid Photochemical mineralization of 4-nitrophenol to14CO2. Paraoxon-methyl and 4-nitrophenol formation was mainly mediated by the combination of light, O3, and -OH radicals. In radish experiments PM photodegradation was presumably located in the cuticle compartment, which exhibited a sensitized photodegradation, as more unknown Products were yielded compared to the glass and soil dust experiments. This could be explained by intensifying the inherent PM degradation in the dark with the same Product spectrum. Due to Photochemical Product formation, which is an antagonistic process to the volatilization of parent compound, the volatilization of unaltered parathion-methyl from each surface generally decreased in the presence of light, particularly in combination with increasing O3 concentrations and OH radical Production rates. First results demonstrated that the photovolatility chamber provides a special tool for the systematic evaluation of (a) photodegradation of surface-located pesticide residues, i.e. measuring qualitative aspects of direct and indirect photodegradation together with relative photodegradation rates, and (b) volatilization of pesticides on surfaces by including and optionally varying relevant parameters such as light, atmospheric O3 concentration, surface temperature, air temperature, air flow rate. The experimental facility represents an important complement to lysimeter and field studies, in particular for experiments on the volatilization of pesticides using the wind tunnel system. With the photovolatiliry chamber special experiments on photodegradation, volatilization and plant uptake can be conducted to study key processes in more detail and this will lead to a better understanding of the effects of certain environmental processes on the fate of released agrochemicals contributing to an improved risk assessment.