TPP and singlet oxygen quenching by carotene in solution

Antioxidant properties of naturally occurring species, β-carotene, are investigated by examining its ability to quench singlet oxygen (1O2) 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 (3TPP) and 1O2. Dependencies of lifetimes of 3TPP and 1O2 on concentration of β-carotene were established as well as quenching rate constants for β-carotene. Hypothesis of multi-component 3TPP is proposed and investigated. Quenching constant of (10.9±0.5)×109M−1s−1 for bimolecular quenching of 1O2 by β-carotene and quenching constant of (8±3)×109M−1s−1 for bimolecular quenching of 3TPP longer lived component were determined.