Scavenging of photogenerated singlet molecular oxygen and superoxide radical anion by sulpha drugs - Kinetics and mechanism

2004 ◽  
Vol 82 (12) ◽  
pp. 1752-1759 ◽  
Author(s):  
Marta Díaz ◽  
Marta Luiz ◽  
Sonia Bertolotti ◽  
Sandra Miskoski ◽  
Norman A García
Keyword(s):  
Visible Light ◽  
Ground State ◽  
Radical Anion ◽  
Superoxide Radical ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Singlet Molecular Oxygen ◽  
Superoxide Radical Anion ◽  
Sulpha Drugs

The ability of the sulfanilic antibiotics (SDs), dapsone (DAP), sulfisoxazole (SFX), sulfadiazine (SFD), and sulfanilic acid (SFNA) to act as scavengers of the visible-light-photogenerated species superoxide radical anion (O2·–) and singlet molecular oxygen (O2(1Δg)) was studied employing the natural pigment riboflavin (Rf) and the artificial dye Rose Bengal as photosensitisers. A complex mechanism, common to all the SDs studied, was elucidated through stationary photolysis, polarographic detection of oxygen uptake, fluorescence spectroscopy, time-resolved phosphorescence detection of O2(1Δg), and laser flash photolysis. Visible-light irradiation of aqueous and aqueous methanolic solutions of Rf (ca. 0.02 mmol/L) plus SD (ca. 0.5 mmol/L) photogenerated excited singlet and triplet Rf (1Rf* and 3Rf*). Under these experimental conditions, only 3Rf* is quenched either by oxygen, giving rise to O2(1Δg) by electronic energy transfer to dissolved ground-state oxygen, or by SD, yielding semireduced Rf through an electron-transfer process. Complementary experiments performed in pure water employing superoxide dismutase and sodium azide inhibition of oxygen uptake, in parallel with laser flash photolysis data, showed that O2·– is also formed, probably due to the reaction of the anion radical from Rf with dissolved oxygen, yielding also neutral, ground-state Rf. Both active oxygen species, namely, O2·– and O2(1Δg), are quenched by the SDs and, as a result, photodegradation of the SDs — each to a different extent — and photodegradation of the sensitiser itself were observed. The SDs that kinetically behave as the better physical quenchers of O2(1Δg), which are in principle good candidates as photoprotectors, namely, DAP and SFD, suffer photooxidation, exhibiting high to moderate oxygen consumption rates due to the O2·– oxidative pathway, whereas for SFNA and SFX, oxidation predominantly occurs through an O2(1Δg)-mediated mechanism. Microbiological results for SFX, taken as a representative SD, indicate that the photodegradation of the drug, upon visible-light Rf-sensitised irradiation, is accompanied by a net loss in bacteriostatic activity.Key words: photooxidation, singlet oxygen, superoxide radical anion, sulpha drugs.

scholarly journals Onium salts improve the kinetics of photopolymerization of acrylate activated with visible light

RSC Advances ◽  
2020 ◽  
Vol 10 (42) ◽  
pp. 24817-24829 ◽  
Author(s):  
Janina Kabatc ◽  
Katarzyna Iwińska ◽  
Alicja Balcerak ◽  
Dominika Kwiatkowska ◽  
Agnieszka Skotnicka ◽  
...  
Keyword(s):  
Steady State ◽  
Visible Light ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Nanosecond Laser ◽  
Chemical Mechanisms ◽  
Onium Salts ◽  
Nanosecond Laser Flash Photolysis ◽  
Kinetics Of

The chemical mechanisms were investigated by steady state photolysis and nanosecond laser flash photolysis experiments. A mechanism for initiating polymerization using both onium salts is proposed here.

Mutual effects between aromatic amino acids and guanosine upon vitamin B2 photosensitization in the presence of visible light

2013 ◽  
Vol 91 (8) ◽  
pp. 684-690
Author(s):  
M. Paulina Montaña ◽  
Gabriela Ferrari ◽  
Eduardo Gatica ◽  
José Natera ◽  
Walter Massad ◽  
...  
Keyword(s):  
Amino Acids ◽  
Visible Light ◽  
Superoxide Radical ◽  
Marked Decrease ◽  
Aromatic Amino Acids ◽  
Quantum Yields ◽  
Vitamin B2 ◽  
Singlet Molecular Oxygen ◽  
Superoxide Radical Anion ◽  
The Individual

Considering the importance of the visible-light-induced photodynamic effect in complex bioenvironments, mutual effects between the individual aromatic amino acids (AAs) tyrosine (Tyr), tryptophan (Trp), and histidine (His) and the nucleoside guanosine (GUO) were investigated in pH 7 aqueous solution with vitamin B2 (riboflavin (Rf)) as a dye sensitizer. The quantum yields of oxygen uptake (Φ–O2) for most of the AA−GUO mixtures studied, taken as a measure of overall photooxidation susceptibility, are not straightforwardly predictable from the individual behaviour of the components of the mixture. The final result depends on several connected factors, such as the respective abilities of the substrates as quenchers of the long-lived Rf triplet excited state and the generated reactive oxygen species singlet molecular oxygen (O2(1Δg)) and superoxide radical anion ([Formula: see text]). A mechanistic interpretation of the Rf-sensitized results can be roughly resumed as follows: Tyr at pH 7 exerts a protective effect on the photooxidation of the mixture Tyr−GUO due to the O2(1Δg) physical quenching by the AA. The same effect was observed for Trp−GUO and His−GUO at pH 7. In these cases, it is attributed to the quenching of 3Rf* by GUO in detriment of the Type II route. For the system Tyr−GUO at pH 9, a marked decrease in the Φ–O2 occurred for the mixture as compared with the respective Φ–O2 for the individual components. It was ascribed to the participation of a radical-mediated mechanism without oxygen consumption in a competitive pathway with the [Formula: see text]-mediated route.

Synthesis and Characterization of Novel Platinum Acetylide Oligomers

2003 ◽  
Vol 771 ◽  
Author(s):  
Thomas M. Cooper ◽  
Benjamin C. Hall ◽  
Daniel G. McLean ◽  
Joy E. Rogers ◽  
Aaron R. Burke ◽  
...  
Keyword(s):  
Absorption Spectra ◽  
Ground State ◽  
Near Infrared ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Structure Property ◽  
Ground State Absorption ◽  
Excitation Spectra ◽  
C Nmr

AbstractAs part of an effort to develop a spectroscopic structure-property relationship in platinum acetylide oligomers, we have prepared a series of bidentate Pt(PBu3)2L2 compounds. The ligand was the series o-syd-C6H4-CΞC-(C6H4-CΞC)n-H, n = 0,1,2. The terminal oligomer unit consisted of a sydnone group ortho to the acetylene carbon. The compounds were characterized by various methods, including 13C-NMR, ground state absorption, fluorescence, phosphorescence and laser flash photolysis. The acetylenic 13C-NMR resonances showed sydnone influences that decreased with increasing number of monomer units. The ground state absorption spectra were slightly red shifted from those of the baseline oligomers not having a sydnone group. The low temperature emission and excitation spectra showed complex dependence on excitation and emission wavelengths, suggesting the chromphores resided in a distribution of solvent environments and conformations. Finally, broad triplet state absorption spectra were observed, with absorption throughout the visible and near infrared regions.

Visible light superoxide radical anion generation by tetra(4-carboxyphenyl)porphyrin/TiO2: EPR characterization

2010 ◽  
Vol 215 (2-3) ◽  
pp. 172-178 ◽  
Author(s):  
Carlos E. Diaz-Uribe ◽  
Martha C. Daza ◽  
Fernando Martínez ◽  
Edgar A. Páez-Mozo ◽  
Carmen L.B. Guedes ◽  
...  
Keyword(s):  
Visible Light ◽  
Radical Anion ◽  
Superoxide Radical ◽  
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.

scholarly journals Time-Resolved Study of Light-Induced Ground State Proton Transfer from Acid Medium to 4-Nitrophenolate

2020 ◽  
Author(s):  
Leandro Scorsin ◽  
Leticia Martins ◽  
Haidi Fiedler ◽  
Faruk Nome ◽  
RENE NOME
Keyword(s):  
Acetic Acid ◽  
Proton Transfer ◽  
Electronic State ◽  
Ground State ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Proton Transfer Reaction ◽  
Ground Electronic State ◽  
Experimental Conditions

In the present work, we study the transient laser-induced formation of 4-nitrophenolate (4-NPO<sup>-</sup>) in the ground electronic state and subsequent proton transfer reaction with acetic acid and water with numerical calculations and laser flash photolysis. We employ the Debye-Smoluchowski spherically-symmetric diffusion model of photoacid proton transfer to determine experimental conditions for studying thermally activated chemical reactions in the ground electronic state. Numerically calculated protonation and deprotonation probabilities for 4-NPO<sup>-</sup> and 4-nitrophenol (4-NPOH) in both ground and excited states showed the feasibility of efficiently producing the ground state anion in the photoacid cycle. We performed laser flash photolysis measurements of 4-NPOH to characterize the photo-initiated ground state protonation and deprotonation rate constants of 4-NPO<sup>-</sup>/4-NPOH as a function of acetic acid, pH, temperature and viscosity. Overall, the work presented here shows a simple way to study fast competing bimolecular proton transfer reactions in non-equilibrium conditions in the ground electronic state <i>(GSPT)</i>.

Superoxide Radical Anion‐Mediated Aerobic Oxidative Synthesis of 2‐Substituted Quinazolines under Visible Light

2017 ◽  
Vol 6 (4) ◽  
pp. 449-452 ◽  
Author(s):  
Xiu‐Long Yang ◽  
Qing‐Yuan Meng ◽  
Xue‐Wang Gao ◽  
Tao Lei ◽  
Cheng‐Juan Wu ◽  
...  
Keyword(s):  
Visible Light ◽  
Radical Anion ◽  
Superoxide Radical ◽  
Superoxide Radical Anion
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