Rate Constants for the Decay and Reactions of the Lowest Electronically Excited Singlet State of Molecular Oxygen in Solution. An Expanded and Revised Compilation

Abstract

An expanded and revised compilation on the reactivity of singlet oxygen, the lowest electronically excited singlet state of molecular oxygen, 1 O 2 *(1 ∆ g), in fluid solution is presented, which supersedes the publication of Wilkinson and Brummer, J. Phys. Chem. Ref. Data 10: 809 (1981). Rate constants for the chemical reaction and physical deactivation of singlet oxygen available through 1993 have been critically compiled. Solvent deactivation rates (k d) are tabulated for 145 solvents or solvent mixtures and second-order rate constants for interaction of singlet oxygen with 1915 compounds are reported.

Singlet Oxygen in a Cell: Spatially Dependent Lifetimes and Quenching Rate Constants

“…Quenching rate constants, k q , over the range ~ 3-6 × 10 8 s -1 M -1 have been reported for experiments performed in aqueous systems, and a value as large as 5 × 10 9 s -1 M -1 has been reported for CH 3 CN. 44 Although these values of k q are slightly less than the rate constant expected for a diffusion-limited process in a solvent whose viscosity is approximately 1 mPa s (i.e., k diff ~ 1-3 × 10 10 s -1 M -1 ), 45 the quenching of singlet oxygen by NaN 3 should readily approach the diffusion-controlled limit as the viscosity of the surrounding medium is increased. Although this viscosity-dependent phenomenon is general, it has been explicitly demonstrated for the quenching of singlet oxygen in a number of polymer-based systems.…”

“…This number is consistent with those reported for the quenching of singlet oxygen by other porphyrin-based systems. 44 If we assume that the magnitude of this rate constant does not change appreciably with solvent, then we can use it to estimate that an intracellular Chl concentration of ~ 0.2 mM would lead to the observed change in the singlet oxygen lifetime from 17 ± 2 µs to 4.5 ± 0.5 µs.…”

“…44 A more general explanation for the NaN 3 quenching data is that there could be domain-dependent local gradients in the intracellular NaN 3 concentration. However, the validity of this interpretation still relies on the significant fact that the diffusion of singlet oxygen from one subcellular domain to another must be restricted due, principally, to a comparatively high intracellular viscosity.…”

Photophysical properties and intracellular imaging of water-soluble porphyrin dimers for two-photon excited photodynamic therapy

“…= 0.74) in water as standards. 6 The fluorescence quantum yields were determined relative to chla (! f = 0.32 in ether) 34 and verteporfin (!…”

“…The singlet oxygen quantum yields of clinical photosensitisers vary from 0.1 to 1.0 and are strongly solvent dependent. 6 The efficiency of singlet oxygen generation by a hydrophobic sensitiser can be severely compromised in an aqueous environment due to aggregation, thereby leading to a lower PDT 55 efficiency. The cellular response to PDT also depends on the primary organelle targeted by the photosensitiser.…”