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

• Published in: Canadian journal of chemistry Vol. 82; no. 12; pp. 1752 - 1759
• Main Authors: Díaz, Marta, Luiz, Marta, Bertolotti, Sonia, Miskoski, Sandra, García, Norman A
• Format: Journal Article
• Language: English
• Published: Ottawa, Canada NRC Research Press 01.12.2004; Canadian Science Publishing NRC Research Press
• Subjects: Absorption; Antibiotics; Dissolved oxygen; Energy transfer; Fluorescence; Ions; Irradiation; Kinetics; Molecules; Oxidation; Oxygen; Oxygen consumption; Oxygen uptake; Photodegradation; Photolysis; Photooxidation; Sodium
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/v04-146

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 (O 2 · – ) and singlet molecular oxygen (O 2 ( 1 Δ g )) 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 O 2 ( 1 Δ g ), 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 ( 1 Rf* and 3 Rf*). Under these experimental conditions, only 3 Rf* is quenched either by oxygen, giving rise to O 2 ( 1 Δ g ) 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 O 2 · – 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, O 2 · – and O 2 ( 1 Δ g ), 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 O 2 ( 1 Δ g ), which are in principle good candidates as photoprotectors, namely, DAP and SFD, suffer photooxidation, exhibiting high to moderate oxygen consumption rates due to the O 2 · – oxidative pathway, whereas for SFNA and SFX, oxidation predominantly occurs through an O 2 ( 1 Δ g )-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.