Singlet oxygen (1O2) (1O2)

Singlet oxygen (1O2) is a highly reactive, electronically excited state of molecular oxygen that serves as the primary cytotoxic agent in photodynamic therapy (PDT) (Source: NIH National Cancer Institute). It is generated in biological systems primarily through Type II photosensitization, where a light-activated photosensitizer transfers energy to ground-state triplet oxygen (Source: PubChem CID 290). Due to its high reactivity and short diffusion distance, singlet oxygen predominantly targets molecules in its immediate vicinity, particularly the polyunsaturated fatty acids and proteins found in biological membranes (Source: Girotti, A. W., J. Photochem. Photobiol. B, 1990). This interaction initiates lipid peroxidation cascades and protein cross-linking, which compromise membrane integrity and lead to the inactivation of essential membrane-bound enzymes (Source: Kochevar, I. E., Photochem. Photobiol., 1987). These cellular disruptions ultimately trigger programmed cell death pathways, such as apoptosis, or direct necrosis in targeted tissues. While its destructive capacity is harnessed to treat conditions like cancer and age-related macular degeneration, singlet oxygen is also a significant mediator of oxidative stress and light-induced skin aging (Source: Di Mascio, P., et al., Methods Enzymol., 1994). Therapeutic strategies involving singlet oxygen focus on the localized delivery of photosensitizers to minimize off-target damage to healthy biological membranes.

Other names

1O2Singlet molecular oxygenDioxideneExcited state molecular oxygen1Δg oxygenBiological membranes and singlet oxygen

Singlet oxygen is generated via energy transfer from a photosensitizer to molecular oxygen; it then reacts with double bonds in membrane lipids and amino acid residues, causing structural damage and cell death.