Abstract
Antioxidant properties of naturally occurring species, beta-carotene, are investigated by examining its ability to quench singlet oxygen ((1)O(2)) and triplet states of photosensitizer 5,10,15,20-tetraphenyl-porphin (TPP) in tetrahydrofuran solutions. Concentrations of all species are biologically relevant.
The quenching is evaluated using direct spectral- and temporal-resolved detection of weak near-infrared phosphorescence of both triplet TPP ((3)TPP) and (1)O(2). Dependencies of lifetimes of 3TPP and (1)O(2) on concentration of beta-carotene were established as well as quenching rate constants for beta-carotene.
Hypothesis of multicomponent (3)TPP is proposed and investigated. Quenching constant of (10.9 +/- 0.5) x 10(9) M(-1) s(-1) for bimolecular quenching of (1)O(2) by beta-carotene and quenching constant of (8 +/- 3) x 10(9) M(-1) s(-1) for bimolecular quenching of (3)TPP longer lived component were determined.