- Influence of hydroxypropyl-β-cyclodextrin on photo-induced free radical production by the sunscreen agent, butyl-methoxydibenzoylmethane
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The aim of the study was to investigate the effect of hydroxypropyl-β-cyclodextrin (HP-β-CD) on the photo-induced production of free radicals by the sunscreen agent, butyl-methoxydibenzoylmethane (BMDBM). Spin-trapping/electron paramagnetic resonance spectroscopy was used to evaluate the formation of radicals and the extent of BMDBM photodegradation was measured by high-performance liquid chromatography. The stable 2,2,6,6-tetramethylpiperidine-1-oxyl, nitroxide radical (TEMPO) was used as spin-trap. Any free radicals generated during irradiation of the sunscreen agent will couple with the TEMPO radicals giving diamagnetic species and thus a decrease of the signal intensity in the electron paramagnetic resonance spectrum. Following 2-h illumination with simulated sunlight, the solution containing free BMDBM exhibited a 93.9% decrease of the intensity of the TEMPO signal. Under the same irradiation conditions, only a 12.2% reduction of the TEMPO concentration was measured in the sample containing BMDBM complexed with HP-β-CD. Moreover, the decrease of the spin-trap level observed for the HP-β-CD/BMDBM complex was not significantly different from that produced when solutions containing TEMPO only or TEMPO in the presence of HP-β-CD alone were subjected to irradiation. In addition, the photodegradation of the sunscreen agent was reduced by complexation with HP-β-CD (the extent of degradation was 27.6% for the complex compared with 63.1% for free BMDBM). The results obtained indicate that the free radicals generated by BMDBM when exposed to simulated sunlight are effectively scavenged by inclusion complexation of the sunscreen agent with HP-β-CD.
- Scalia,Simeoni,Barbieri,Sostero
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- Methoxy-monobenzoylmethane protects human skin against uv-induced damage by conversion to avobenzone and radical scavenging
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Avobenzone, one of the most commonly used UV filters in topical sunscreens, is susceptible to photodegradation with a consequential reduction of its UV absorbing properties. This loss of function may lead to skin irritation, photodermatosis, and photoallergic reactions caused by photodegradation byproducts. In this work, we aim to address this issue with a substance named methoxy-monobenzoylmethane (MeO-MBM), which is neither a UVB nor a UVA filter, but which converts to avobenzone, a known and approved UVA filter, under mainly UVB light irradiation. The antioxidant and intracellular radical formation properties of MeO-MBM were compared to the ones of avobenzone. The UV irradiation of MeO-MBM led to an increase in UV absorption primarily in the UVA range after conversion, both in vitro and in vivo. HPTLC and UHPLC studies illustrate the conversion of MeO-MBM to avobenzone in vitro after irradiation at 250 kJ/m2, reaching a conversion rate of 48.8%. A stable molecular antioxidant activity was observed, since 100-μM MeOMBM was measured to be 11.2% in the DPPH assay, with a decrease to 9.7% after irradiation. In comparison, the molecular antioxidant activity of 100-μM avobenzone was determined to be 0.8%. In keratinocytes, MeO-MBM reduces the intracellular ROS by 90% and avobenzone by 75% with tBHP as the inducer and by 53% and 57%, respectively, when induced by pyocyanin, indicating the redox scavenging capacity of both these molecules. These results indicate that MeO-MBM functions initially as an antioxidant material and as a photoantioxidant during its conversion process to avobenzone. This research provides insight into the development of active ingredients for topical applications with dynamic functionalities. Using this approach, we demonstrate the possibility to extend the UV protection offered to skin cells while combating cellular stress in parallel.
- Carola, Christophe,Keck, Cornelia M.,Salazar, Andrew,Termer, Michael,von Hagen, Joerg
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- Ester-Activated Vinyl Ethers as Chain Transfer Agents in Radical Photopolymerization of Methacrylates
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The regulation of multifunctional methacrylates to yield tough photopolymers is a widely researched topic, whereby addition-fragmentation chain transfer (AFCT) agents represent one viable class of additives. Vinyl ethers have been described as potent AFCT agents in radical polymerization but are unexamined in network formation via photopolymerization. In this article, we present a sterically hindered vinyl ether as AFCT agent for methacrylate networks, which shows enhanced acid stability opposed to vinyl ethers described in the literature. After synthesis and confirmation of the efficient regulation in a monofunctional system, the reactivity and mechanical properties in a difunctional methacrylate were evaluated. An increase in double bond conversion, significantly lower shrinkage stress, and high toughness were assessed and substantiated the great potential of this compound in photopolymerizable resins.
- Peer, Gernot,Eibel, Anna,Gorsche, Christian,Catel, Yohann,Gescheidt, Georg,Moszner, Norbert,Liska, Robert
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p. 2691 - 2700
(2019/03/29)
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- Kinetic Study of the Phthalimide N-Oxyl Radical in Acetic Acid. Hydrogen Abstraction from Substituted Toluenes, Benzaldehydes, and Benzyl Alcohols
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The phthalimide N-oxyl (PINO) radical was generated by the oxidation of N-hydroxyphthalimide (NHPI) with Pb(OAc)4 in acetic acid. The molar absorptivity of PINO. is 1.36 × 103 L mol -1 cm-1 at λmax 382 nm. The PINO radical decomposes slowly with a second-order rate constant of 0.6 ± 0.1 L mol-1 s-1 at 25°C. The reactions of PINO . with substituted toluenes, benzaldehydes, and benzyl alcohols were investigated under an argon atmosphere. The second-order rate constants were correlated by means of a Hammett analysis. The reactions with toluenes and benzyl alcohols have better correlations with σ+ (ρ = -1.3 and -0.41), and the reaction with benzaldehydes correlates better with σ (ρ = -0.91). The kinetic isotope effect was also studied and significantly large values of kH/kD were obtained: 25.0 (p-xylene), 27. 1 (toluene), 27.5 (benzaldehyde), and 16.9 (benzyl alcohol) at 25°C. From the Arrhenius plot for the reactions with p-xylene and p-xylene-d10, the difference of the activation energies, EaD - E aH, was 12.6 ± 0.8 kJ mol-1 and the ratio of preexponential factors, AH/AD, was 0.17 ± 0.05. These findings indicate that quantum mechanical tunneling plays an important role in these reactions.
- Koshino, Nobuyoshi,Saha, Basudeb,Espenson, James H.
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p. 9364 - 9370
(2007/10/03)
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- Modulation of lifetimes and diastereomeric discrimination in triplet- excited substituted butane-1,4-diones through intramolecular charge-transfer quenching
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Triplet lifetimes have been determined for the diastereomers of a broad set of butane-1,4-dione derivatives (1-3). A remarkable dependence of lifetimes on conformational preferences is revealed in that the lifetimes are shorter for the meso diastereomers of 1-3 than those for the racemic ones. The intramolecular β-phenyl quenching is promoted in the case of meso diastereomers by virtue of the gauche relationship between the excited carbonyl group and the β-aryl ring, while a distal arrangement in the lowest energy conformation (H-anti) in racemic diastereomers prevents such a deactivation. The involvement of charge transfer in the intramolecular β- phenyl quenching is suggested by the correlation of the triplet lifetimes of the meso diastereomers of compounds 2 with the nature of the substituent on the β-phenyl rings. In the case of racemic diastereomers, p-methoxy substitution on the β-phenyl ring (2-OCH3, 3-OCH3) also led to a decrease of the triplet lifetimes when compared to those of the nonsubstituted compounds (2-H, 3-H). This shortening is accounted for by the deactivation of a small proportion of the excited molecules through β-phenyl quenching. In addition to the above factors, the lifetimes in the case of meso diastereomers can further be controlled by increasing the energy spacing between the T1 and T2 states, since β-phenyl quenching occurs from the latter for compounds 2 and 3. Through a rational conformational control, a surprisingly long triplet lifetime (300 ns) has been measured for the first time for a purely n,π* triplet-excited β-phenylpropiophenone dimer (1- rac).
- Moorthy,Monahan,Sunoj,Chandrasekhar,Bohne
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p. 3093 - 3103
(2007/10/03)
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- Kinetic and Spectroscopic Studies on Acyl Radicals in Solution by Time-Resolved Infrared Spectroscopy
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A number of acyl radicals, R=O, have been generated in hexane or di-t-butyl peroxide as solvent at room temperature by 308 nm laser flash photolysis, and their spectroscopic and kinetic properties have been examined by time-resolved infrared spectroscopy.The C=O stretching frequencies for the R=O radicals are found to be higher than those of the corresponding aldehydes, RCHO, by between 108 and 128 cm-1, an effect attributed to a higher C=O bond order in the radicals.For the R=O radicals some typical values of νC=O are: CH3=O, 1864 cm-1; (CH3)3C=O, 1848 cm-1; and C6H5=O, 1828 cm-1, while the corresponding acylperoxyl radicals, RC(O)OO, formed by reaction with oxygen have νC=O values of 1838, 1840 and 1820 cm-1, respectively.The acyl radicals exhibit a reactivity towards a variety of substrates that is roughly comparable to that of simple alkyl radicals.For reactions of the benzoyl radical some typical rate constants/M-1s-1 are: CCl4, 6.0*104; C6H5SH, 4.8*107; CCl3Br, 2.2*108; Tempo, 1.1+109; and oxygen, 1.8*109.Alkanoyl radicals have a rather similar reactivity to benzoyl.The propanoyl radical reacts with tributyltin deuteride with a rate constant of 3*105 M-1s-1.The hex-5-enoyl radical undergoes a 5-exo-trig cyclization to form the 2-oxocyclopentylmethyl radical with a rate constant of 2.2*105 s-1, a value which is almost identical to that for cyclization of the hex-5-enyl radical.It is hoped that our kinetic data will prove useful in the planning of organic synthetic strategies which involve acyl radical chemistry.
- Brown, Carl E.,Neville, Anthony G.,Rayner, David M.,Ingold, Keith U.,Lusztyk, Janusz
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p. 363 - 380
(2007/10/02)
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- EPR Studies on the Photofragmentation of 2,2-Dialkyl-2-alkylaminoacetophenones
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Free radical reactions induced by photolysis of 2,2-dialkyl-2-aminoacetophenone photocuring agents have been studied by continuous wave (CW) and time-resolved EPR spectroscopy.In all solvents α-cleavage from the triplet state is the major process.In hydrogen donor solvents it is accompanied by photoreduction followed by a rapid amine elimination from the ketyl radical intermediate.The benzoyl and α-aminoalkyl radicals resulting from α-cleavage readily add to acrylonitrile whereas radicals formed by photoreduction do not.
- Leopold, Detlev,Fischer, Hanns
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p. 513 - 518
(2007/10/02)
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- Kinetics for Reaction of the Nitrate Radical (NO3.) with aldehydes in Acetone in Acetonitrile
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The rate constants for the reactions of NO3. with RCHO (R: H, CH3, C2H5, CH(CH3)2, and C(CH3)3 and XC6H4CHO (X: NO2, CN, Cl, H, and OCH3) have been measured by following the decay of the transient absorption band of NO3. generated by photolysis of K2 in acetonitrile.Representative rate constants (in unit of M-1 s-1) at 20 deg C in acetonitrile are 2.3E7 for CH3CHO and 2.4E7 for PhCHO.The hydrogen-atom abstraction reaction of NO3. from the aldehydic C-H was confirmed by the similarity of the above two rate constants and by the higher reactivites than those of acetone and benzene.The rate constants for HCHO and CH3CHO in aqueous solution are smaller than the corresponding values in acetonitrile, because of the hydration.For aliphatic aldehydes, the methyl substitution on the vicinal carbon to aldehydic carbon slightly increase the reactivity of the aldehydic C-H with NO3..A large negative Hammett reaction constant (ρ=-1.3) for aryl aldehydes indicates the high electrophilicity of NO3..The polar substituents stronly affect the orientation factors rather than the activation energies, which were obtained by the Arrhenius plots.The rate constants in acetonitrile, however, are ca. 30 times larger than the corresponding ones reported in the gas phase: a polar mediun affects the distribution of an unpaired electron and the polar nature of the reaction.
- Ito, Osamu,Akiho, Seiji,Iino, Masashi
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p. 4079 - 4083
(2007/10/02)
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- Benzoyl ?-Radicals: the Barrier to Internal Rotation
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Rotational barriers of some para-substituted benzoyl radicals have been measured by e.s.r. techniques: the linear correlation between the e.s.r. ΔG(excit.) values and the corresponding n.m.r. ΔG(excit.) values allows us to estimate the free energy of activation of the unsubstituted benzoyl radical -1 (11.8 +/- 0.6 kJ mol-1)>.
- Grossi, Loris,Placucci, Giuseppe
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p. 943 - 944
(2007/10/02)
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