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Miguel A. Miranda - One of the best experts on this subject based on the ideXlab platform.
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Sunscreen-Based Photocages for Topical Drugs: A Photophysical and Photochemical Study of A Diclofenac-Avobenzone Dyad.
Molecules (Basel Switzerland), 2018Co-Authors: Isabel Aparici-espert, Miguel A. Miranda, Virginie Lhiaubet-valletAbstract:Photosensitization by drugs is a problem of increasing importance in modern life. This phenomenon occurs when a chemical substance in the skin is exposed to sunlight. Photosensitizing drugs are reported to cause severe skin dermatitis, and indeed, it is generally advised to avoid sunbathing and to apply sunscreen. In this context, the nonsteroidal anti-inflammatory drug (NSAID) diclofenac is a photosensitive drug, especially when administered in topical form. In this work, efforts have been made to design and study an innovative pro-drug/pro-filter system containing diclofenac and the UVA filter Avobenzone in order to develop a safer use of this topical drug. The design is based on the presence of a well-established photoremovable phenacyl group in the Avobenzone structure. Steady-state photolysis of the dyad in hydrogen-donor solvents, monitored by UV-Vis spectrophotometry and HPLC, confirms the simultaneous photorelease of diclofenac and Avobenzone. Laser flash photolysis and phosphorescence emission experiments allow us to gain insight into the photoactive triplet excited-state properties of the dyad. Finally, it is shown that Avobenzone provides partial photoprotection to diclofenac from photocyclization to carbazole derivatives.
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Photocages for protection and controlled release of bioactive compounds
Chemical communications (Cambridge England), 2016Co-Authors: Isabel Aparici-espert, Virginie Lhiaubet-vallet, Cecilia Paris, M. C. Cuquerella, Miguel A. MirandaAbstract:Using a sunscreen-based photocage, we have demonstrated that it is possible to prevent photodegradation of a bioactive compound and to achieve its controlled photorelease. The concept has been proven linking Avobenzone, one of the most important UVA blockers, to ketoprofen, which is a representative example of a photosensitive drug.
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Photochemical and photophysical properties of dibenzoylmethane derivatives within protein
Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, 2011Co-Authors: M. L. Marin, Cecilia Paris, Virginie Lhiaubet-vallet, Minoru Yamaji, Miguel A. MirandaAbstract:In the present work, three dibenzoylmethane derivatives in their β-diketo form have been selected to investigate their photophysical and photochemical behavior upon interaction with human serum albumin (HSA). In organic solvents, absorption and phosphorescence emission spectra of the α-bromo derivative of Avobenzone (BrAB) were similar to those of the α-methylated and α-propyl analogs (MeAB and PrAB). However, laser flash photolysis experiments revealed a different transient species centered at 350 nm, assigned to the radical obtained from a singlet excited state dehalogenation process. Interestingly, the transient absorption spectrum of BrAB within HSA showed the typical features of the β-diketone triplet excited state. In the case of MeAB and PrAB derivatives, binding to HSA was associated with a significant increase of their triplet lifetimes as compared to acetonitrile. Finally, the Norrish type II process has been considered as a model to evaluate the influence of the protein microenvironment on the photoreactivity. In this context, photodegradation of PrAB in aerated solutions, to give Avobenzone (AB), has been monitored by UV spectroscopy. Interestingly, the quantum yields of AB formation were markedly dependent on the reaction medium (1.4 × 10−2 in acetonitrile and 3.9 × 10−2 within albumin medium); by contrast, chemical yields of ca. 50% were obtained in both cases.
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Steady-state and laser flash photolysis studies on photochemical formation of 4-tert-butyl-4′-methoxydibenzoylmethane from its derivative via the Norrish Type II reaction in solution
Journal of Photochemistry and Photobiology A-chemistry, 2009Co-Authors: Minoru Yamaji, Cecilia Paris, Miguel A. MirandaAbstract:Abstract A photochemical formation process of Avobenzone (AB; 4-tert-butyl-4′-methoxydibenzoylmethane) from 1,1-(4-tert-butybenzoyl)(4′-methoxybenzoyl)butane (PrAB) is studied by steady-state and laser flash photolysis in solution. The quantum yield of the formation via the triplet state of PrAB is determined to be 0.23 in degassed acetonitrile at 295 K. The Arrhenius plots of the decay rate of triplet PrAB show that photoelimination proceeds with an activation energy of 6.0 kcal mol−1 and the frequency factor of 4.6 × 1010 s−1.
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a blocked diketo form of Avobenzone photostability photosensitizing properties and triplet quenching by a triazine derived uvb filter
Photochemistry and Photobiology, 2009Co-Authors: Cecilia Paris, Oscar Jiménez, Carles Trullas, Virginie Lhiaubetvallet, Miguel A. MirandaAbstract:Novel sunscreens are required providing active protection in the UVA and UVB regions. On the other hand, there is an increasing concern about the photosafety of UV filters, as some of them are not sufficiently photostable. Avobenzone is one of the most frequently employed sunscreen ingredients, but it has been reported to partially decompose after irradiation. In the present work, photophysical and photochemical studies on a methylated Avobenzone-derivative have shown that the diketo form is responsible for photodegradation. A transient absorption was observed at 380 nm after laser flash photolysis excitation at 308 nm. It was assigned to the triplet excited state of the diketo form, as inferred from quenching by oxygen and β-carotene. This transient also interacted with key building blocks of biomolecules by triplet–triplet energy transfer (in the case of thymidine) or electron transfer processes (for 2′-deoxyguanosine, tryptophan and tyrosine). Irradiation of the Avobenzone derivative in the presence of a triazine UV-B filter (E-35852) diminished the undesirable effects of the compound by an efficient quenching of the triplet excited state. Thus, sunscreen formulations including triplet quenchers could provide effective protection from the potential phototoxic and photoallergic effects derived from poor photostability of Avobenzone.
Bice S. Martincigh - One of the best experts on this subject based on the ideXlab platform.
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3-(3,4,5-Trimethoxybenzylidene)-2,4-pentanedione: Design of a novel photostabilizer with in vivo SPF boosting properties and its use in developing broad-spectrum sunscreen formulations.
International journal of cosmetic science, 2016Co-Authors: Ratan K. Chaudhuri, Moses A. Ollengo, Parvesh Singh, Bice S. MartincighAbstract:Objective The study concerned the synthesis of a novel photostabilizer based on benzylidenepentanedione chemistry and the evaluation of its potential in developing a broad-spectrum sunscreen formulation containing Avobenzone. Methods 3-(3,4,5-Trimethoxybenzylidene)-2-4-pentanedione (TMBP) was synthesized through a condensation reaction and incorporated into a sunscreen formulation containing, inter alia, Avobenzone. The SPF, critical wavelength and in vitro photostability of the product were measured. The photostability was compared with that afforded by current Avobenzone photostabilizers, namely octocrylene, ethylhexylmethoxycrylene and diethylhexylsyringylidenemalonate. The photostability of TMBP either alone or in the presence of Avobenzone in a methanolic solution was also evaluated by UV spectrophotometric and HPLC analyses. The optical properties of TMBP were estimated experimentally and supported by time-dependent density functional theory (TD-DFT) calculations. Results The ability of TMBP to stabilize Avobenzone under ultraviolet (UV) light exposure was shown both in formulated products and in solution. A comparative stability study incorporating various combinations of Avobenzone, TMBP (vs. three commercial photostabilizers) and UVB sunscreens clearly showed TMBP to be a very effective stabilizer. The photostabilizing effect of TMBP arises from triplet-state energy transfer from Avobenzone to TMBP and through light-induced reactions that preserve the main chromophores. Interestingly, a 50% in vivo SPF boosting was observed when TMBP was used with organic and inorganic sunscreens when alone it has no contribution to SPF. TMBP-containing sunscreen formulations clearly showed a critical wavelength of well over 370 nm and can thus be categorized as broad-spectrum sunscreens. Conclusion We were able to design a very effective photostabilizer, trimethoxybenzylidene pentanedione (INCI name), based on benzylidenepentanedione chemistry. TMBP is very efficient in stabilizing Avobenzone in formulated products and boosts in vivo SPF by >50% for organic and inorganic sunscreens, and the formulations have critical wavelengths of >370 nm. These efficacious properties make it a promising additive for inclusion in broad-spectrum photoprotective products.
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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.
Thomas A Meyer - One of the best experts on this subject based on the ideXlab platform.
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characterization of the uva protection provided by Avobenzone zinc oxide and titanium dioxide in broad spectrum sunscreen products
American Journal of Clinical Dermatology, 2010Co-Authors: Donathan G Beasley, Thomas A MeyerAbstract:Background: Solar UV radiation (UVR) is composed of UVB (290–320 nm) and UVA (320–400 nm) wavelengths. Only two sunscreen active ingredients approved in the US, Avobenzone (butylmethoxydibenzoylmethane) and zinc oxide (ZnO), provide true broad-spectrum protection against UVA wavelengths >360 nm. Although effective against shorter UVR wavelengths <360 nm, titanium dioxide (TiO2) is also often believed to confer broad-spectrum protection and is substituted for ZnO or Avobenzone. To sustain its absorption capacity within a sunscreen film during UVR exposure, Avobenzone needs to be formulated into sunscreen products using sound formulation strategies. Objectives: To characterize the efficacy of Avobenzone, ZnO, and TiO2 in terms of their abilities to provide broad UVA protection and to demonstrate the effectiveness of the different formulation strategies used today to maintain the efficacy of Avobenzone even during prolonged exposures to UVR. Methods: UVA efficacy was assessed by measuring absorbance profiles in vitro using Vitro Skin® (IMS Inc., Orange, CT, USA) as an inert substrate and by determining UVA protection factors (PFA) on human skin. The impact of Avobenzone loss on sun protection factor (SPF) and PFA values was evaluated by serially reducing Avobenzone concentrations in an otherwise photostable product. The photostabilizing influence of specific formulation ingredients was monitored by measuring the extent to which they prevented UVRinduced degradation of Avobenzone, whereas photostability of commercial sunscreen products was quantified by measuring the percentage change in absorbance within the UVB and UVA spectral regions following irradiation of thin product films on inert substrates. Results: Model formulations containing 3% Avobenzone or 5% ZnO provided superior attenuation of UVA wavelengths >360 nm compared with formulas containing 5% TiO2. Additionally, sunscreen products of similar SPF containing Avobenzone or ZnO exhibited significantly higher PFA values than those containing TiO2. The addition of photostabilized Avobenzone or ZnO increased PFA values nearly 3-fold, whereas the addition of TiO2 increased PFA values only modestly. Judicious selection of sunscreen actives alone or in combination with extra stabilizing agents maintained the photostability of Avobenzone in formulations to deliver sustained broad-spectrum absorbance during 4 hours of exposure to UVR. Small losses (<20%) of Avobenzone did not significantly reduce a product’s protective effects as measured by SPF and PFA values on human skin. Conclusions: TiO2 provided neither the same level ofUVA attenuation nor the same degree of UVA protection on human skin as did products containing photostabilized Avobenzone or ZnO. Hence, TiO2 cannot be considered a substitute for Avobenzone or ZnO in providing high levels of UVA protection to human skin.Use of proper formulation strategies can ensure that Avobenzone losses are minimized to the extent that they have no impact on a product’s ability to deliver sustained protection, even over periods of prolonged exposure to UVR.
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Characterization of the UVA Protection Provided by Avobenzone, Zinc Oxide, and Titanium Dioxide in Broad-Spectrum Sunscreen Products
American Journal of Clinical Dermatology, 2010Co-Authors: Donathan G Beasley, Thomas A MeyerAbstract:Background: Solar UV radiation (UVR) is composed of UVB (290–320 nm) and UVA (320–400 nm) wavelengths. Only two sunscreen active ingredients approved in the US, Avobenzone (butylmethoxydibenzoylmethane) and zinc oxide (ZnO), provide true broad-spectrum protection against UVA wavelengths >360 nm. Although effective against shorter UVR wavelengths 360 nm compared with formulas containing 5% TiO_2. Additionally, sunscreen products of similar SPF containing Avobenzone or ZnO exhibited significantly higher PFA values than those containing TiO_2. The addition of photostabilized Avobenzone or ZnO increased PFA values nearly 3-fold, whereas the addition of TiO_2 increased PFA values only modestly. Judicious selection of sunscreen actives alone or in combination with extra stabilizing agents maintained the photostability of Avobenzone in formulations to deliver sustained broad-spectrum absorbance during 4 hours of exposure to UVR. Small losses (
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.
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An investigation of the photostabilisation of sunscreen absorbers by plant polyphenols.
2005Co-Authors: Georges J. MturiAbstract:Commercial sunscreen products are used to protect the skin against hannful ultraviolet (UV) radiation that can induce skin cancer at high dosage. These products contain UV filters that can reflect, scatter or absorb UV light. The chemical UV filters responsible for the absorption of UV radiation can be photochemically modified and as a result reduce the efficacy of the sunscreen formulation. This study focused on the possible use ofplant polyphenols as potential stabilisers of photo-unstable sunscreen chemical absorbers. The photo-instability of some sunscreen absorbers results in radical formation; this prompted the use of the plant, Sutherlandia microphylla (Cancer Bush plant), as a potential photostabiliser. The Cancer Bush plant is used by the indigenous people of South Africa to treat AIDS and cancer. The radical scavenging properties of polyphenolic compounds present in the plant are possibly responsible for the plant's anti-tumour and anti-IDV properties. Therefore, these Cancer Bush polyphenols could possibly be used to photostabilise photo-unstable sunscreen absorbers. Potential polyphenolic photostabilisers from the Cancer Bush plant were extracted by means of various polyphenolic extraction methods. These extracts were analysed by gas chromatography (GC), high-performance liquid chromatography (HPLC), UV spectroscopy and gas chromatography-mass spectrometry (GC-MS). The phenolic content and the antioxidant activity ofthese extracts were investigated by means of the Folin-eiocalteu reagent (FCR) and the diphenylpicrylhydrazyl (DPPH) radical assays respectively. Polyphenols were also extracted from various Rooibos teas and compared with those extracted from the Cancer Bush plant. Both the Cancer Bush and various Rooibos tea extracts were found to contain simple phen~lics and potential polyphenolic compounds. The Cancer Bush extracts as well as the Rooibos tea extracts together with the specific polyphenols, epicatechin and rutin, were assessed for their ability to photostabilise sunscreen absorbers. The photostability of the chemical absorbers in the absence and in the presence of the polyphenol extracts was investigated by UV spectroscopy, by monitoring their absorption spectra during irradiation with solar-simulated radiation. These extracts inhibited the photodegradation of the absorber Avobenzone. The photostability of Avobenzone is solventIntroduction III dependent hence the investigations were carried out in three solvents, namely, cyclohexane, ethyl acetate and dimethylsulfoxide. Additionally, the cause ofthe instability ofAvobenzone in these solvents was investigated by means of DV spectroscopy, HPLC and nuclear magnetic resonance spectroscopy. The oxygen dependency of the photo-instability of Avobenzone was also determined. The photo-instability of Avobenzone was found to occur as a result of photoisomerisation and!or photodegradation, depending on the solvent. Avobenzone photoisomerised extensively in dimethylsulfoxide and photodegraded appreciably in cyclohexane, whereas both processes occurred to…
Cecilia Paris - One of the best experts on this subject based on the ideXlab platform.
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Photocages for protection and controlled release of bioactive compounds
Chemical communications (Cambridge England), 2016Co-Authors: Isabel Aparici-espert, Virginie Lhiaubet-vallet, Cecilia Paris, M. C. Cuquerella, Miguel A. MirandaAbstract:Using a sunscreen-based photocage, we have demonstrated that it is possible to prevent photodegradation of a bioactive compound and to achieve its controlled photorelease. The concept has been proven linking Avobenzone, one of the most important UVA blockers, to ketoprofen, which is a representative example of a photosensitive drug.
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Photochemical and photophysical properties of dibenzoylmethane derivatives within protein
Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, 2011Co-Authors: M. L. Marin, Cecilia Paris, Virginie Lhiaubet-vallet, Minoru Yamaji, Miguel A. MirandaAbstract:In the present work, three dibenzoylmethane derivatives in their β-diketo form have been selected to investigate their photophysical and photochemical behavior upon interaction with human serum albumin (HSA). In organic solvents, absorption and phosphorescence emission spectra of the α-bromo derivative of Avobenzone (BrAB) were similar to those of the α-methylated and α-propyl analogs (MeAB and PrAB). However, laser flash photolysis experiments revealed a different transient species centered at 350 nm, assigned to the radical obtained from a singlet excited state dehalogenation process. Interestingly, the transient absorption spectrum of BrAB within HSA showed the typical features of the β-diketone triplet excited state. In the case of MeAB and PrAB derivatives, binding to HSA was associated with a significant increase of their triplet lifetimes as compared to acetonitrile. Finally, the Norrish type II process has been considered as a model to evaluate the influence of the protein microenvironment on the photoreactivity. In this context, photodegradation of PrAB in aerated solutions, to give Avobenzone (AB), has been monitored by UV spectroscopy. Interestingly, the quantum yields of AB formation were markedly dependent on the reaction medium (1.4 × 10−2 in acetonitrile and 3.9 × 10−2 within albumin medium); by contrast, chemical yields of ca. 50% were obtained in both cases.
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Steady-state and laser flash photolysis studies on photochemical formation of 4-tert-butyl-4′-methoxydibenzoylmethane from its derivative via the Norrish Type II reaction in solution
Journal of Photochemistry and Photobiology A-chemistry, 2009Co-Authors: Minoru Yamaji, Cecilia Paris, Miguel A. MirandaAbstract:Abstract A photochemical formation process of Avobenzone (AB; 4-tert-butyl-4′-methoxydibenzoylmethane) from 1,1-(4-tert-butybenzoyl)(4′-methoxybenzoyl)butane (PrAB) is studied by steady-state and laser flash photolysis in solution. The quantum yield of the formation via the triplet state of PrAB is determined to be 0.23 in degassed acetonitrile at 295 K. The Arrhenius plots of the decay rate of triplet PrAB show that photoelimination proceeds with an activation energy of 6.0 kcal mol−1 and the frequency factor of 4.6 × 1010 s−1.
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a blocked diketo form of Avobenzone photostability photosensitizing properties and triplet quenching by a triazine derived uvb filter
Photochemistry and Photobiology, 2009Co-Authors: Cecilia Paris, Oscar Jiménez, Carles Trullas, Virginie Lhiaubetvallet, Miguel A. MirandaAbstract:Novel sunscreens are required providing active protection in the UVA and UVB regions. On the other hand, there is an increasing concern about the photosafety of UV filters, as some of them are not sufficiently photostable. Avobenzone is one of the most frequently employed sunscreen ingredients, but it has been reported to partially decompose after irradiation. In the present work, photophysical and photochemical studies on a methylated Avobenzone-derivative have shown that the diketo form is responsible for photodegradation. A transient absorption was observed at 380 nm after laser flash photolysis excitation at 308 nm. It was assigned to the triplet excited state of the diketo form, as inferred from quenching by oxygen and β-carotene. This transient also interacted with key building blocks of biomolecules by triplet–triplet energy transfer (in the case of thymidine) or electron transfer processes (for 2′-deoxyguanosine, tryptophan and tyrosine). Irradiation of the Avobenzone derivative in the presence of a triazine UV-B filter (E-35852) diminished the undesirable effects of the compound by an efficient quenching of the triplet excited state. Thus, sunscreen formulations including triplet quenchers could provide effective protection from the potential phototoxic and photoallergic effects derived from poor photostability of Avobenzone.
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A Blocked Diketo Form of Avobenzone: Photostability, Photosensitizing Properties and Triplet Quenching by a Triazine‐derived UVB‐filter
Photochemistry and photobiology, 2008Co-Authors: Cecilia Paris, Virginie Lhiaubet-vallet, Oscar Jiménez, Carles Trullas, Miguel A. MirandaAbstract:Novel sunscreens are required providing active protection in the UVA and UVB regions. On the other hand, there is an increasing concern about the photosafety of UV filters, as some of them are not sufficiently photostable. Avobenzone is one of the most frequently employed sunscreen ingredients, but it has been reported to partially decompose after irradiation. In the present work, photophysical and photochemical studies on a methylated Avobenzone-derivative have shown that the diketo form is responsible for photodegradation. A transient absorption was observed at 380 nm after laser flash photolysis excitation at 308 nm. It was assigned to the triplet excited state of the diketo form, as inferred from quenching by oxygen and β-carotene. This transient also interacted with key building blocks of biomolecules by triplet–triplet energy transfer (in the case of thymidine) or electron transfer processes (for 2′-deoxyguanosine, tryptophan and tyrosine). Irradiation of the Avobenzone derivative in the presence of a triazine UV-B filter (E-35852) diminished the undesirable effects of the compound by an efficient quenching of the triplet excited state. Thus, sunscreen formulations including triplet quenchers could provide effective protection from the potential phototoxic and photoallergic effects derived from poor photostability of Avobenzone.
