Physical Mechanisms of Generation and Deactivation of Singlet Oxygen

Abstract

IV. Photosensitized Production of Singlet Oxygen 1721 A. Oxygen Quenching of Excited Triplet States 1725 1. Parameters Influencing the Generation of Singlet Oxygen 1725 2. Mechanism of Oxygen Quenching of ππ* Triplet States 1731 3. Mechanism of Oxygen Quenching of nπ* Triplet States 1736 B. Oxygen Quenching of Excited Singlet States 1737 1. Rate Constants of S 1 -State Quenching 1737 2. Products of S 1 -State Quenching 1739 3. Mechanism of Oxygen Quenching of Excited Singlet States 1742 V. Detection of Singlet Oxygen 1745 VI. Applications 1746 A. Estimation of the a f X Radiative Rate Constant in Different Environments 1746 1. Liquid Phase 1747 2. Gas Phase 1747 3. Microheterogeneous Systems 1747 B. Estimation of the Contribution of e−v, CT, EET, and Chemical Pathways to O 2 ( 1 ∆ g ) and O 2 ( 1 Σ g + ) Deactivation 1748 C. Estimation of O 2 ( 1 ∆ g ) and O 2 ( 1 Σ g + ) Lifetimes in Different Environments 1749 1. Liquid Phase 1749 2. Polymers 1749 3. Gas Phase 1749 4. Microheterogeneous Systems 1749 5. Zeolite Systems 1750 D. Estimation of a f X Emission Quantum Yields 1750 E. e−v Deactivation of Isoelectronic Molecules 1750 F. Optimization of Singlet Oxygen Sensitizers 1750 G. Estimation of Singlet Oxygen Diffusion Lengths 1752 VII. Conclusion 1752 VIII. Acknowledgment 1752 IX. References 1752

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

“…It is also well-established that (i) changes in the concentration of dissolved oxygen only influence k T , not k rem (an exception occurs only in solvents where the inherent lifetime of singlet oxygen is extraordinarily long; e.g., CCl 4 or CS 2 ), and (ii) changes in the H/D isotopic composition of the surrounding medium only influence k rem , not k T . 2,15 In the present study, we used both direct triplet state measurements The insets show plots of the rate constant for singlet oxygen removal, k rem , against the concentration of NaN 3 (i.e., Eq. 2).…”

“…[1][2][3] It is wellestablished that singlet oxygen is an oxidizing/oxygenating agent for a wide range of organic molecules. 1,4 Production of sufficient quantities of singlet oxygen in a biological environment can perturb cellular processes, and can ultimately cause cell death via apoptosis or necrosis.…”

“…[8][9][10][11] A common and convenient way to produce singlet oxygen is photosensitization. 2 In this process, a molecule (the so-called sensitizer or, in PDT, the added drug) absorbs light to populate an excited state. Most efficient sensitizers readily produce a long-lived triplet state which transfers its energy of excitation to the ground state of molecular oxygen, O 2 (X 3 Σ g -), in a collision-dependent process.…”

“…2 In our work on single cells thus far, we have exploited the latter to enhance the intensity of the singlet oxygen phosphorescence signal detected. Specifically, the lifetime of singlet oxygen in D 2 O is ~ 67…”

“…2 16 In most of our previous singlet oxygen work in cells, we used a hydrophilic cationic porphyrin as a photosensitizer: 5,10,15,20-tetrakis(N-methyl-4-pyridyl)-21H, 23H-porphine (TMPyP). This molecule tends to accumulate in the nucleus of cells, but an appreciable amount can still be found in the cytoplasm.…”