Quenching of the Excited States of 2‐phenylbenzoxazole by Azide Anion. Fluorescence and Esr Study

Reszka, Krzysztof J.; Hall, Robert D.; Chignell, Colin F.

doi:10.1111/j.1751-1097.1984.tb04641.x

Cited by 19 publications

(9 citation statements)

References 32 publications

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“…The oxidizing properties of both PBSA and PBI are clearly shown by their reactions with azide. Sodium azide reacts with photoexcited PBSA to form the azidyl radical and quenches PBSA fluorescence with a rate constant of 4.46 ϫ 10 9 M Ϫ1 s Ϫ1 , consistent with values reported earlier (18). This rate constant for PBSA reflects a strong interaction between the singlet excited state of PBSA and the azide anion and strongly suggests that the excited singlet state of PBSA is oxidizing in nature.…”

Section: Photooxidizing Propertiessupporting

confidence: 88%

“…We examined the potential of the excited singlet state of PBSA to accept electrons by measuring its fluorescence in the presence of sodium azide. Sodium azide has been shown to quench the fluorescence of a compound structurally similar to PBI, namely, 2-phenylben-zoxazole (2-PBO) (18). It was suggested that this quenching could be caused by electron transfer from the azide anion to the singlet state of 2-PBO.…”

Section: Photochemistrymentioning

confidence: 99%

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Photophysical and Photochemical Studies of 2-Phenylbenzimidazole and UVB Sunscreen 2-Phenylbenzimidazole-5-sulfonic Acid¶

Inbaraj¹,

Bilski²,

Chignell³

2002

Photochem Photobiol

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The sunscreen agent 2-phenylbenzimidazole-5-sulfonic acid (PBSA) and its parent 2-phenylbenzimidazole (PBI) cause DNA photodamage via both Type-I and Type-II mechanisms when UVB irradiated. We have studied the photophysical and photochemical properties of these compounds and their ability to photogenerate reactive oxygen species including free radicals. PBI and PBSA exhibit both oxidizing and reducing properties in their excited state. The absorption and fluorescence properties of PBSA depend strongly upon pH, and hence the photochemistry of PBSA was studied in both neutral and alkaline solutions. PBSA showed strong oxidizing properties when UV irradiated in neutral aqueous solution (pH 7.4) in the presence of cysteine, glutathione and azide, as evidenced by the detection of the corresponding S-cysteinyl, glutathiyl and azidyl radicals with the aid of the spin trap, 5,5-dimethyl-1-pyrroline N-oxide (DMPO). However, when an aqueous anaerobic solution (pH 10) of PBSA and either nitromethane (NM) or 4-nitrobenzoic acid (4-NBA) were irradiated, the corresponding nitro anion radicals were observed. This finding suggests that both NM and 4-NBA are reduced by direct electron transfer from the excited state PBSA. During UV irradiation of an aerobic solution of PBSA, O2*- and *OH radical were generated and trapped by DMPO. Further, PBI (in ethanol) and PBSA (in ethylene glycol : water 2: 1 mixture) showed low temperature (77 K) phosphorescence (lambdamax = 443, 476 and 509 nm) and also an electron paramagnetic resonance half-field transition (deltaMs = +/-2), which is evidence for a triplet state. This triplet produced singlet oxygen (1O2) with quantum yields 0.07 and 0.04 in MeCN for PBI and PBSA, respectively. These studies demonstrate that UV irradiation of PBSA and PBI generates a variety of free radicals and active oxygen species that may be involved in the photodamage of DNA.

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Section: Photooxidizing Propertiessupporting

confidence: 88%

Section: Photochemistrymentioning

confidence: 99%

Photophysical and Photochemical Studies of 2-Phenylbenzimidazole and UVB Sunscreen 2-Phenylbenzimidazole-5-sulfonic Acid¶

Inbaraj¹,

Bilski²,

Chignell³

2002

Photochem Photobiol

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“…A similar, photoinduced decay of nitroxide radicals in the presence of photosensitizers has been reported previously. [32] We also observed the decay of TEMPOL in a separate set of experiments, where we worked with intentionally oxygen-depleted aqueous solutions of various fullerene-based photosensitizers (data not shown). Therefore, the marked change in the ESR signal intensity of TEM-POL observed after 25 min of illumination ( Fig.…”

Section: Full Papermentioning

confidence: 93%

Spectroscopic and Photophysical Properties of a Highly Derivatized C₆₀ Fullerol

Vileno

Marcoux

Lekka

et al. 2005

Adv Funct Materials

128

151

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Hydroxylated C60 molecules, also called fullerols, are a class of water‐soluble fullerenes. Here we report the synthesis in acidic conditions of a highly derivatized fullerol (up to 36 carbons per C60 are oxidized). Spectroscopic investigations (X‐ray photoelectron spectroscopy and infrared absorption) highlight the coexistence of both acidic and basic forms for the hydroxyl addends of derivatized C60. pH titrimetry reveals that, at millimolar concentrations, only ten protons per fullerol molecule are labile. Such a low value, as compared to 36 hydroxyl groups, is explained by the formation of clusters. A UV‐vis absorption study performed over a large range of concentrations also points to the aggregation phenomenon. Moreover, this study shows that the clusters of fullerols appear at relatively low (micromolar) concentrations. An electron spin resonance (ESR) study, based on the attack of singlet oxygen (1Δg) on 2,2,6,6‐tetramethyl‐4‐piperidinol (TMP‐OH), has proved the potential of hydroxylated C60 for performing efficient generation of singlet oxygen in aqueous solution. ESR measurements, which allow detection and quantification of 1Δg, have also revealed the generation of reactive oxygen species (ROS). The yield of generation of 1Δg and ROS is strongly correlated to the concentration of fullerol, thus also pointing to the aggregation of fullerol molecules. Exposing glioblastoma cells to oxidative stress in the presence of hydroxylated C60 and visible light has also been performed. Atomic force microscopy is used to monitor the relevant diminishment of the Young's modulus values for cells exposed to the oxidative stress. These results point to a possible application field of fullerols for performing bio‐oxidations.

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“…The sulfur analogues of alkoxyl radicals (thiyls) are also trapped at fast rate constants (-lo8 M-I s-' ) (13). spin trapping studies have suggested that oxygen-centered radicals may be important intermediates in radiolysis (14) and sonolysis (15) reactions, ozone-related chemistry (16,17), xanthinelxanthine oxidase systems (18), carcinogenesis (19), antitumour drug redox interactions (20)(21)(22), cigarette smoke (23), druglskin phototoxicity (24,25), neutrophil action (26a-c), peroxidation reactions (27)(28)(29)(30)(31), as well as myocardial ischemia/reperfusion injury (32a-c).…”

mentioning

confidence: 99%

The first ¹H and ¹⁴N ENDOR spectra of an oxygen-centered radical adduct of DMPO-type nitrones

Haire¹,

Oehler²,

Goldman³

et al. 1988

Can. J. Chem.

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. Can. J. Chem. 66, 2395 (1988). ~, We report the first 'H and ' 4~ electron nuclear double resonance (ENDOR) spectra of oxygen-centered radical adducts (i.e.,derived from the addition of tert-butoxyl radicals) of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as well as the related cyclic nitrones: 4-phenyl-5,5-dimethyl-1-pyrroline-N-oxide (4-Ph-DMPO) and 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO).Features of the electron paramagnetic resonance (EPR) and ENDOR spectra of these cyclic (pyrrolidine) aminoxyl (nitroxide) species along with some deuterated analogues in liquid toluene solutions are highlighted. For instance, we found several long-range y-H hyperfine splittings (HFS's) detectable by ENDOR that provide unique spectral signatures for these radical adducts. Conformational assignments of the pyrrolidine aminoxyl structures based upon the EPR and ENDOR findings are also discussed. Signs of the various hyperfine splittings (i.e., aN, a;, a : ) investigated by cross-relaxation intensity sequence patterns (CRISP) in the ENDOR spectra are also presented. [Traduit par la revue]

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Quenching of the Excited States of 2‐phenylbenzoxazole by Azide Anion. Fluorescence and Esr Study

Cited by 19 publications

References 32 publications

Photophysical and Photochemical Studies of 2-Phenylbenzimidazole and UVB Sunscreen 2-Phenylbenzimidazole-5-sulfonic Acid¶

Photophysical and Photochemical Studies of 2-Phenylbenzimidazole and UVB Sunscreen 2-Phenylbenzimidazole-5-sulfonic Acid¶

Spectroscopic and Photophysical Properties of a Highly Derivatized C₆₀ Fullerol

The first ¹H and ¹⁴N ENDOR spectra of an oxygen-centered radical adduct of DMPO-type nitrones

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Quenching of the Excited States of 2‐phenylbenzoxazole by Azide Anion. Fluorescence and Esr Study

Cited by 19 publications

References 32 publications

Photophysical and Photochemical Studies of 2-Phenylbenzimidazole and UVB Sunscreen 2-Phenylbenzimidazole-5-sulfonic Acid¶

Photophysical and Photochemical Studies of 2-Phenylbenzimidazole and UVB Sunscreen 2-Phenylbenzimidazole-5-sulfonic Acid¶

Spectroscopic and Photophysical Properties of a Highly Derivatized C60 Fullerol

The first 1H and 14N ENDOR spectra of an oxygen-centered radical adduct of DMPO-type nitrones

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Spectroscopic and Photophysical Properties of a Highly Derivatized C₆₀ Fullerol

The first ¹H and ¹⁴N ENDOR spectra of an oxygen-centered radical adduct of DMPO-type nitrones