Singlet Oxygen Generation by 8-Methoxypsoralen in Deuterium Oxide:  Relaxation Rate Constants and Dependence of the Generation Efficacy on the Oxygen Partial Pressure

Abstract

The photoactivation of 8-methoxypsoralen (8-MOP) by ultraviolet light is widely used for the treatment of several skin diseases. The major mechanism is the intercalation of 8-MOP into nuclear DNA in the dark and subsequently the formation of monoadducts and potential cross links under UVA irradiation. In addition, the irradiation of 8-MOP leads to the generation of singlet oxygen by means of photodynamic action which has been shown to induce a critical oxidative damage of the DNA in vitro. To assess the role of singlet oxygen generated by photoactivated 8-MOP, its relaxation in solutions of deuterium oxide was studied in detail. Relaxation rates and rate constants of the involved 8-MOP triplet T 1 state and oxygen 1 ∆ g state were determined by analyzing the rise and decay rates of the luminescence of singlet oxygen at 1.27 µm. The efficacy of singlet oxygen generation is described by the singlet oxygen quantum yield Φ ∆ , which depends on the efficacy of 8-MOP T 1 state deactivation by oxygen, P T ([O 2 ]). P T ([O 2 ]) has been determined for different oxygen concentrations and decreased from 2% under aerated conditions (e.g., in vitro conditions, 130 Torr) to 0.5% for the in ViVo situation inside the skin (∼20 Torr). The efficacy of singlet oxygen generation and maybe therefore the role of singlet oxygen in the oxidative damage depends critically on the respective oxygen partial pressure. This must be considered when transferring results and conclusions from experiments in vitro or in solution to the situation in vivo.

The role of singlet oxygen and oxygen concentration in photodynamic inactivation of bacteria

“…Recently, a model was developed to estimate the singlet oxygen dose by characterization of Photofrin (Axcan Pharma, Birmingham, AL) photobleaching during photodynamic therapy of eukaryotic cells in vitro (18). Moreover, singlet oxygen can be visualized by measuring its luminescence at 1,270 nm directly in solvents (19,20), in eukaryotic cells (21,22), and even in human skin (23). This time-resolved decay of the luminescence should provide an indication of the site of singlet oxygen in bacteria.…”

Spectroscopic investigation on protein damage by ciprofloxacin under ultrasonic irradiation

“…There are many reports about the detection method of ROS, such as redox probes method used to investigate oxidative stress in cellular systems [33], measuring 1 O 2 luminescence method [34] and colorimetric techniques [35]. However, these methods require not only the high cost but also advanced equipment, and are not widely used to investigate ROS in routine laboratory.…”

Time‐resolved Singlet Oxygen Phosphorescence Measurements from Photosensitized Experiments in Single Cells: Effects of Oxygen Diffusion and Oxygen Concentration

“…For the T 1photosensitized production of O 2 (a 1 D g ), the evolution of the O 2 (a 1 D g ) phosphorescence signal, P, in time should behave according to Eq. (2) (8,11,19,27):…”

“…The effect of the ambient oxygen partial pressure on both the time evolution and intensity of O 2 (a 1 Δ g ) phosphorescence signals in photosensitized experiments has been examined in detail for a variety of sensitizers in homogeneous liquid solutions (4,10,11). The data reflect the expected effect that, at low oxygen concentrations, the frequency of collisions between O 2 (X 3 Σ g − ) and the T 1 state will be less.…”

“…Kinetics of singlet oxygen formation and decay. For the T 1 ‐photosensitized production of O 2 (a 1 Δ g ), the evolution of the O 2 (a 1 Δ g ) phosphorescence signal, P , in time should behave according to (8,11,19,27): where K is a scaling parameter that includes the efficiency of O 2 (a 1 Δ g ) production, k T is the rate constant for all channels of T 1 deactivation ( i.e. k q [O 2 (X 3 Σ g − )] + k 0 ) and k d is the rate constant that correspondingly accounts for all deactivation channels of O 2 (a 1 Δ g ).…”