Contribution of the Excited Triplet State of Humic Acid and Superoxide Radical Anion to Generation and Elimination of Phenoxyl Radical

2018 ◽  
Vol 52 (15) ◽  
pp. 8283-8291 ◽  
Author(s):  
Yuan Chen ◽  
Xu Zhang ◽  
Shixiang Feng
Keyword(s):  
Humic Acid ◽  
Triplet State ◽  
Radical Anion ◽  
Superoxide Radical ◽  
Phenoxyl Radical ◽  
Excited Triplet State ◽  
Excited Triplet ◽  
Superoxide Radical Anion

The activity of 3- and 7-hydroxyflavones as scavengers of superoxide radical anion generated from photo-excited riboflavin

2003 ◽  
Vol 81 (8) ◽  
pp. 909-914 ◽  
Author(s):  
Paulina Montaña ◽  
Nora Pappano ◽  
Nora Debattista ◽  
Vicente Ávila ◽  
Ariana Posadaz ◽  
...  
Keyword(s):  
Molecular Oxygen ◽  
Excited States ◽  
Radical Anion ◽  
Superoxide Radical ◽  
Chemical Transformations ◽  
Singlet Molecular Oxygen ◽  
Electron Transfer Process ◽  
Excited Triplet ◽  
Superoxide Radical Anion ◽  
Oxidative Species

The visible-light irradiation of the system Rivoflavin plus 3-hydroxyflavone or plus 7-hydroxyflavone, under aerobic conditions, produces a series of competitive processes that depend on the relative concentrations of the pigment and the flavones. The picture comprises photochemical mechanisms that potentially operate in nature. They mainly include the quenching of Rf singlet (1Rf*) and triplet (3Rf*) excited states (with bimolecular rate constants in the order of 109 M–1 s–1) and superoxide radical anion-mediated reactions. The participation of the oxidative species singlet molecular oxygen was not detected. The overall result shows chemical transformations in both Rf and 3-hydroxyflavone. No experimental evidence was found indicating any chemical reaction involving 7-hydroxyflavone. The fate of the pigment also depends on the amount of the dissolved flavonoid. At 50 mM concentrations of these compounds or higher, practically no photochemistry occurs, owing to the extensive quenching of 1Rf*. When the concentration of the flavones is in the mM range or lower, 3Rf* is photogenerated. Then, the excited triplet species can be quenched mainly by the flavones through an electron-transfer process, yielding the semireduced pigment. The latter interacts with dissolved oxygen producing O2·–, which reacts with both the pigment and 3-hydroxyflavone. In summary, 3-hydroxyflavone and 7-hydroxyflavone participate in the generation of superoxide ion in an Rf-sensitized process, and simultaneously 3-hydroxyflavone constitutes a degradable quencher of the oxidative species.Key words: flavones, riboflavin, sensitization, singlet molecular oxygen, superoxide radical anion.

Aromaticity Reversal in the Lowest Excited Triplet State of Archetypical Möbius Heteroannulenic Systems

2016 ◽  
Vol 128 (22) ◽  
pp. 6597-6601 ◽  
Author(s):  
Juwon Oh ◽  
Young Mo Sung ◽  
Woojae Kim ◽  
Shigeki Mori ◽  
Atsuhiro Osuka ◽  
...  
Keyword(s):  
Triplet State ◽  
Excited Triplet State ◽  
Excited Triplet
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