Singlet-oxygen generation from A2E

Area of Science:

• Photochemistry
• Biochemistry
• Ophthalmology

Background:

• Retinal lipofuscins, such as A2E and its isomer iso-A2E, accumulate in the eye with age.
• These compounds are implicated in age-related macular degeneration due to their photosensitizing properties.

Purpose of the Study:

• To quantify singlet oxygen generation by A2E and iso-A2E.
• To compare the singlet oxygen generation efficiency of these lipofuscins with a known photosensitizer, tetraphenylporphine (TPP).
• To investigate the influence of solvent dielectric constant on singlet oxygen production.

Main Methods:

• Steady-state irradiation of A2E and iso-A2E in various deuterated solvents.
• Use of cholesterol as a singlet oxygen trap.
• Quantification of singlet oxygen using a known quantum yield for TPP as a reference.

Main Results:

• Singlet oxygen quantum yields for A2E/iso-A2E mixtures were determined in ethanol-d6, acetone-d6, cyclohexane-acetone, and hexafluorobenzene.
• Quantum yields ranged from 0.8 x 10(-3) to 4 x 10(-3) at 420 nm, depending on the solvent.
• Singlet oxygen generation was highest in solvents with the lowest dielectric constants.
• Lower quantum yields were observed at longer wavelengths in acetone-d6.

Conclusions:

• A2E and iso-A2E are capable of generating singlet oxygen upon irradiation.
• The efficiency of singlet oxygen generation is relatively low.
• Solvent polarity significantly affects singlet oxygen production.
• Further investigation is needed to determine the precise contribution of singlet oxygen to the phototoxic effects of A2E and iso-A2E.