The Experts below are selected from a list of 765 Experts worldwide ranked by ideXlab platform
Bice S. Martincigh - One of the best experts on this subject based on the ideXlab platform.
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photostability of the Sunscreening Agent 4 tert butyl 4 methoxydibenzoylmethane avobenzone in solvents of different polarity and proticity
Journal of Photochemistry and Photobiology A-chemistry, 2008Co-Authors: Georges J. Mturi, Bice S. MartincighAbstract:The most widely used UVA absorber in broad-spectrum sunscreens is 4-tert-butyl-4� -methoxydibenzoylmethane (avobenzone). However, the photostability of avobenzone is solvent-dependent. The aim of this work was to investigate the photostability of avobenzone in solvents of different polarity and proticity. Four solvents were employed, namely, cyclohexane, ethyl acetate, dimethylsulfoxide and methanol. The cause of the instability of avobenzone in these solvents was determined by means of UV spectroscopy, high performance liquid chromatography, gas chromatography–mass spectrometry and nuclear magnetic resonance spectroscopy. The effect of oxygen on the photo-instability was also determined. Avobenzone was found to lose absorption efficacy as a result of photoisomerisation from the enol to the keto form and/or photodegradation to form photoproducts that absorb principally in the UVC region, depending on the solvent. It was found to be essentially photostable in the polar protic solvent methanol but photoisomerised in the polar aprotic solvent dimethylsulfoxide. In the nonpolar solvent cyclohexane, it photodegraded appreciably. Both photoisomerisation and photodegradation occurred to a similar extent in the moderately polar aprotic solvent ethyl acetate. Photoisomerisation occurred only in the presence of oxygen whereas photodegradation occurred irrespective of oxygen. This knowledge is important in order to achieve the correct formulation for sunscreens incorporating avobenzone.
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Photostability of the Sunscreening Agent 4-tert-butyl-4′-methoxydibenzoylmethane (avobenzone) in solvents of different polarity and proticity
Journal of Photochemistry and Photobiology A-chemistry, 2008Co-Authors: Georges J. Mturi, Bice S. MartincighAbstract:The most widely used UVA absorber in broad-spectrum sunscreens is 4-tert-butyl-4� -methoxydibenzoylmethane (avobenzone). However, the photostability of avobenzone is solvent-dependent. The aim of this work was to investigate the photostability of avobenzone in solvents of different polarity and proticity. Four solvents were employed, namely, cyclohexane, ethyl acetate, dimethylsulfoxide and methanol. The cause of the instability of avobenzone in these solvents was determined by means of UV spectroscopy, high performance liquid chromatography, gas chromatography–mass spectrometry and nuclear magnetic resonance spectroscopy. The effect of oxygen on the photo-instability was also determined. Avobenzone was found to lose absorption efficacy as a result of photoisomerisation from the enol to the keto form and/or photodegradation to form photoproducts that absorb principally in the UVC region, depending on the solvent. It was found to be essentially photostable in the polar protic solvent methanol but photoisomerised in the polar aprotic solvent dimethylsulfoxide. In the nonpolar solvent cyclohexane, it photodegraded appreciably. Both photoisomerisation and photodegradation occurred to a similar extent in the moderately polar aprotic solvent ethyl acetate. Photoisomerisation occurred only in the presence of oxygen whereas photodegradation occurred irrespective of oxygen. This knowledge is important in order to achieve the correct formulation for sunscreens incorporating avobenzone.
Georges J. Mturi - One of the best experts on this subject based on the ideXlab platform.
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photostability of the Sunscreening Agent 4 tert butyl 4 methoxydibenzoylmethane avobenzone in solvents of different polarity and proticity
Journal of Photochemistry and Photobiology A-chemistry, 2008Co-Authors: Georges J. Mturi, Bice S. MartincighAbstract:The most widely used UVA absorber in broad-spectrum sunscreens is 4-tert-butyl-4� -methoxydibenzoylmethane (avobenzone). However, the photostability of avobenzone is solvent-dependent. The aim of this work was to investigate the photostability of avobenzone in solvents of different polarity and proticity. Four solvents were employed, namely, cyclohexane, ethyl acetate, dimethylsulfoxide and methanol. The cause of the instability of avobenzone in these solvents was determined by means of UV spectroscopy, high performance liquid chromatography, gas chromatography–mass spectrometry and nuclear magnetic resonance spectroscopy. The effect of oxygen on the photo-instability was also determined. Avobenzone was found to lose absorption efficacy as a result of photoisomerisation from the enol to the keto form and/or photodegradation to form photoproducts that absorb principally in the UVC region, depending on the solvent. It was found to be essentially photostable in the polar protic solvent methanol but photoisomerised in the polar aprotic solvent dimethylsulfoxide. In the nonpolar solvent cyclohexane, it photodegraded appreciably. Both photoisomerisation and photodegradation occurred to a similar extent in the moderately polar aprotic solvent ethyl acetate. Photoisomerisation occurred only in the presence of oxygen whereas photodegradation occurred irrespective of oxygen. This knowledge is important in order to achieve the correct formulation for sunscreens incorporating avobenzone.
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Photostability of the Sunscreening Agent 4-tert-butyl-4′-methoxydibenzoylmethane (avobenzone) in solvents of different polarity and proticity
Journal of Photochemistry and Photobiology A-chemistry, 2008Co-Authors: Georges J. Mturi, Bice S. MartincighAbstract:The most widely used UVA absorber in broad-spectrum sunscreens is 4-tert-butyl-4� -methoxydibenzoylmethane (avobenzone). However, the photostability of avobenzone is solvent-dependent. The aim of this work was to investigate the photostability of avobenzone in solvents of different polarity and proticity. Four solvents were employed, namely, cyclohexane, ethyl acetate, dimethylsulfoxide and methanol. The cause of the instability of avobenzone in these solvents was determined by means of UV spectroscopy, high performance liquid chromatography, gas chromatography–mass spectrometry and nuclear magnetic resonance spectroscopy. The effect of oxygen on the photo-instability was also determined. Avobenzone was found to lose absorption efficacy as a result of photoisomerisation from the enol to the keto form and/or photodegradation to form photoproducts that absorb principally in the UVC region, depending on the solvent. It was found to be essentially photostable in the polar protic solvent methanol but photoisomerised in the polar aprotic solvent dimethylsulfoxide. In the nonpolar solvent cyclohexane, it photodegraded appreciably. Both photoisomerisation and photodegradation occurred to a similar extent in the moderately polar aprotic solvent ethyl acetate. Photoisomerisation occurred only in the presence of oxygen whereas photodegradation occurred irrespective of oxygen. This knowledge is important in order to achieve the correct formulation for sunscreens incorporating avobenzone.
Vasilios G. Stavros - One of the best experts on this subject based on the ideXlab platform.
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Photoisomerization of ethyl ferulate: A solution phase transient absorption study
Chemical Physics Letters, 2017Co-Authors: Michael D. Horbury, Lewis A. Baker, Natércia D. N. Rodrigues, Wen-dong Quan, Vasilios G. StavrosAbstract:Abstract Ethyl ferulate (ethyl 4-hydroxy-3-methoxycinnamate) is currently used as a Sunscreening Agent in commercial sunscreen blends. Recent time-resolved gas-phase measurements have demonstrated that it possesses long-lived (>ns) electronic excited states, counterintuitive to what one might anticipate for an effective Sunscreening Agent. In the present work, the photodynamics of ethyl ferulate in cyclohexane, are explored using time-resolved transient electronic absorption spectroscopy, upon photoexcitation to the 11ππ∗ and 21ππ∗ states. We demonstrate that ethyl ferulate undergoes efficient non-radiative decay to repopulate the electronic ground state, mediated by trans-cis isomerization. These results strongly suggest that even mild perturbations induced by a non-polar solvent, as may be found in a closer-to-market sunscreen blend, may contribute to our understanding of ethyl ferulate’s role as a Sunscreening Agent.
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Ultrafast photoprotective properties of the Sunscreening Agent octocrylene
Optics express, 2016Co-Authors: Lewis A. Baker, Michael D. Horbury, Vasilios G. StavrosAbstract:Today octocrylene is one of the most common molecules included in commercially available sunscreens. It provides broadband photoprotection for the skin from incident UV-A and UV-B radiation of the solar spectrum. In order to understand how octocrylene fulfils its role as a Sunscreening Agent, femtosecond pump-probe transient electronic UV-visible absorption spectroscopy is utilised to investigate the ultrafastnonradiative relaxation mechanism of octocrylene in cyclohexane or methanol after UV-B photoexcitation. The data presented clearly shows that UV-B photoexcited octocrylene exhibits ultrafast-nonradiative relaxation mechanisms to repopulate its initial ground state within a few picoseconds, which, at the very least, photophysically justifies its wide spread inclusion in commercial sunscreens.
Lewis A. Baker - One of the best experts on this subject based on the ideXlab platform.
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Understanding electronic energy transport in biologically relevant systems : the photochemistry of sunscreens and the photophysics of photosynthesis
2017Co-Authors: Lewis A. BakerAbstract:This thesis focusses on two areas. The first is elucidating the ultrafast photoprotective mechanisms exhibited by a number of commercial and natural Sunscreening Agents, through the use of femtosecond pump-probe transient absorption spectroscopy, coupled with ab initio electronic structure calculations. The second is understanding the electronic energy transport properties of pigment-protein complexes found in photosynthetic organisms, through the use of quantum dynamics simulations. Oxybenzone, titanium dioxide, octocrylene and ethylhexyl triazone are all studied given their prevalence in commercial sunscreen products. We deduce that oxybenzone relaxes through an enol-keto isomerism (~400 fs) followed by back-isomerisation commensurate with vibration energy transfer to the surrounding solvent (~5-8 ps). Titanium dioxide is then considered in multicomponent suspensions with oxybenzone, where we find that the photodynamics exhibited by each component can be considered independent from one another. Octocrylene is shown to undergo the majority of its photodynamics within ~2 ps, displaying remarkable efficiency as an ultraviolet light chromophore, relaxing through nonradiative internal conversion pathways. Studies of ethylhexyl triazone are presented, where results suggest this molecule relaxes through a number of ultrafast processes, ranging from ~400 fs, ~20 ps and ~200 ps, involving a large change in nuclear geometry, which couples excited states to the ground state through a conical intersection. Sinapoyl malate is the predominant Sunscreening Agent synthesised in arabidopsis thaliana which is deposited into the upper epidermis of its leaves. This molecule, along with its biological precursor sinapic acid, is shown to relax through ultrafast pathways (~10-30 ps), which we suggest is mediated by a trans-cis isomerism, in stark contrast to the recent time-resolved gas-phase measurements indicating the solvent environment alters the photodynamics significantly. Considering the second half of this thesis, we study the Fenna-Matthews-Olson pigment-protein complex found in green sulphur bacteria, and the light-harvesting complex II found in the spinach plant. Employing a simple quantum master equation, the Haken-Strobl model, we highlight a computationally tractable approach for describing these large, complicated systems. To this end, we perform an enormous array of simulations which include a simple description of environmental perturbations and find, for the first time, the full extent of the robustness of these pigment-protein complexes. Most strikingly, for the Fenna-Matthews-Olson complex, we find that up to 50% of the available pigments may be removed, with a small drop of 20% in electronic energy transport, displaying an incredible robustness to network disruption.
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Photoisomerization of ethyl ferulate: A solution phase transient absorption study
Chemical Physics Letters, 2017Co-Authors: Michael D. Horbury, Lewis A. Baker, Natércia D. N. Rodrigues, Wen-dong Quan, Vasilios G. StavrosAbstract:Abstract Ethyl ferulate (ethyl 4-hydroxy-3-methoxycinnamate) is currently used as a Sunscreening Agent in commercial sunscreen blends. Recent time-resolved gas-phase measurements have demonstrated that it possesses long-lived (>ns) electronic excited states, counterintuitive to what one might anticipate for an effective Sunscreening Agent. In the present work, the photodynamics of ethyl ferulate in cyclohexane, are explored using time-resolved transient electronic absorption spectroscopy, upon photoexcitation to the 11ππ∗ and 21ππ∗ states. We demonstrate that ethyl ferulate undergoes efficient non-radiative decay to repopulate the electronic ground state, mediated by trans-cis isomerization. These results strongly suggest that even mild perturbations induced by a non-polar solvent, as may be found in a closer-to-market sunscreen blend, may contribute to our understanding of ethyl ferulate’s role as a Sunscreening Agent.
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Ultrafast photoprotective properties of the Sunscreening Agent octocrylene
Optics express, 2016Co-Authors: Lewis A. Baker, Michael D. Horbury, Vasilios G. StavrosAbstract:Today octocrylene is one of the most common molecules included in commercially available sunscreens. It provides broadband photoprotection for the skin from incident UV-A and UV-B radiation of the solar spectrum. In order to understand how octocrylene fulfils its role as a Sunscreening Agent, femtosecond pump-probe transient electronic UV-visible absorption spectroscopy is utilised to investigate the ultrafastnonradiative relaxation mechanism of octocrylene in cyclohexane or methanol after UV-B photoexcitation. The data presented clearly shows that UV-B photoexcited octocrylene exhibits ultrafast-nonradiative relaxation mechanisms to repopulate its initial ground state within a few picoseconds, which, at the very least, photophysically justifies its wide spread inclusion in commercial sunscreens.
Michael D. Horbury - One of the best experts on this subject based on the ideXlab platform.
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Photoisomerization of ethyl ferulate: A solution phase transient absorption study
Chemical Physics Letters, 2017Co-Authors: Michael D. Horbury, Lewis A. Baker, Natércia D. N. Rodrigues, Wen-dong Quan, Vasilios G. StavrosAbstract:Abstract Ethyl ferulate (ethyl 4-hydroxy-3-methoxycinnamate) is currently used as a Sunscreening Agent in commercial sunscreen blends. Recent time-resolved gas-phase measurements have demonstrated that it possesses long-lived (>ns) electronic excited states, counterintuitive to what one might anticipate for an effective Sunscreening Agent. In the present work, the photodynamics of ethyl ferulate in cyclohexane, are explored using time-resolved transient electronic absorption spectroscopy, upon photoexcitation to the 11ππ∗ and 21ππ∗ states. We demonstrate that ethyl ferulate undergoes efficient non-radiative decay to repopulate the electronic ground state, mediated by trans-cis isomerization. These results strongly suggest that even mild perturbations induced by a non-polar solvent, as may be found in a closer-to-market sunscreen blend, may contribute to our understanding of ethyl ferulate’s role as a Sunscreening Agent.
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Ultrafast photoprotective properties of the Sunscreening Agent octocrylene
Optics express, 2016Co-Authors: Lewis A. Baker, Michael D. Horbury, Vasilios G. StavrosAbstract:Today octocrylene is one of the most common molecules included in commercially available sunscreens. It provides broadband photoprotection for the skin from incident UV-A and UV-B radiation of the solar spectrum. In order to understand how octocrylene fulfils its role as a Sunscreening Agent, femtosecond pump-probe transient electronic UV-visible absorption spectroscopy is utilised to investigate the ultrafastnonradiative relaxation mechanism of octocrylene in cyclohexane or methanol after UV-B photoexcitation. The data presented clearly shows that UV-B photoexcited octocrylene exhibits ultrafast-nonradiative relaxation mechanisms to repopulate its initial ground state within a few picoseconds, which, at the very least, photophysically justifies its wide spread inclusion in commercial sunscreens.
