TPP and singlet oxygen quenching by carotene in solution

Abstract

Antioxidant properties of naturally occurring species, β-carotene, are investigated by examining its ability to quench singlet oxygen ( 1O 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 ( 3TPP) and 1O 2. Dependencies of lifetimes of 3TPP and 1O 2 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) × 10 9 M −1 s −1 for bimolecular quenching of 1O 2 by β-carotene and quenching constant of (8 ± 3) × 10 9 M −1 s −1 for bimolecular quenching of 3TPP longer lived component were determined.