title: Scavenging of photogenerated oxidative species by antimuscarinic drugs: atropine and derivatives.
abstract: The quenching ability of photogenerated oxidative species by some antimuscarinic drugs generically named atropines (e.g. atropine [I] eucatropine [II], homatropine [III] and scopolamine [IV]) have been investigated employing stationary photolysis, polarographic detection of dissolved oxygen, stationary and time-resolved fluorescence spectroscopy, and laser flash photolysis. Using Rose Bengal as a dye sensitiser for singlet molecular oxygen, O(2)((1)Delta(g)), generation, compounds I-IV behave as moderate chemical plus physical quenchers of the oxidative species. Correlation between kinetic and electrochemical data indicates that the process is possibly driven by a charge-transfer interaction. The situation is somewhat more complicated employing the natural pigment riboflavin (Rf) as a sensitiser. Compounds I and II complex Rf ground state, diminishing the quenching ability towards singlet and triplet excited state of the pigment. On the other hand, compounds III and IV effectively quench Rf excited states, protecting the pigment against photodegradation. Under anaerobic conditions, semireduced Rf (Rf(.-)) is formed through quenching of excited triplet Rf. Nevertheless, although Rf(.-) is a well-known generator of the reactive species superoxide radical anion by reductive quenching in the presence of oxygen, the process of O(2)((1)Delta(g)) production prevails over superoxide radical generation, due to the relatively low rate constants for the quenching of triplet Rf by the atropines (in the order of 10(7) M(-1)s(-1) for compounds III and IV) in comparison to the rate constant for the quenching by ground state oxygen, approximately two orders of magnitude higher, yielding O(2)((1)Delta(g)). Compound I is the most promising O(2)((1)Delta(g)) physical scavenger, provided that it exhibits the higher value for the overall quenching rate constant and only 11% of the quenching process leads to its own chemical damage.
authors.affiliation: Departamento de Química, Universidad Nacional de Río Cuarto, 5800 Río Cuarto, Argentina.
authors.forename: Susana
authors.initials: S
authors.lastname: Criado
authors.forename: Carina
authors.initials: C
authors.lastname: Guardianelli
authors.forename: Jimena
authors.initials: J
authors.lastname: Tuninetti
authors.forename: Patricia
authors.initials: P
authors.lastname: Molina
authors.forename: Norman A
authors.initials: NA
authors.lastname: García
mesh_terms: D001285:Atropine / Q000737:chemistry* / Q000378:metabolism*; D004355:Drug Stability; D016166:Free Radical Scavengers / Q000378:metabolism*; D015394:Molecular Structure; D018727:Muscarinic Antagonists / Q000737:chemistry / Q000378:metabolism*; D010782:Photolysis; D017319:Photosensitizing Agents / Q000737:chemistry; D012395:Rose Bengal / Q000737:chemistry; D026082:Singlet Oxygen / Q000737:chemistry / Q000378:metabolism; D013054:Spectrophotometry, Atomic
chemical_list: D016166:Free Radical Scavengers; D018727:Muscarinic Antagonists; D017319:Photosensitizing Agents; D026082:Singlet Oxygen; D012395:Rose Bengal; D001285:Atropine