CHAPTER 3 – Photosensitized Oxidation and Singlet Oxygen: Consequences in Biological Systems

https://science.sciencemag.org/content/sci/162/3857/963.full.pdf

Mechanisms of Photosensitized Oxidation

Siefermann-Harms, D. 1987. The light-harvesting and protective functions of carotenoids in photosynthetic membranes.

The light-harvesting and protective functions of carotenoids in photosynthetic membranes

In a major pathway of the autoxidation of methyl linolenate, peroxyl radicals of the internal hydroperoxides undergo rapid 1,3-tyclisation to form hydroperoxyepidioxides. Because linolenate hydroperoxides are relatively unstable, free radical antioxidants are much less effective in linolenate oils than in linoleate oils. Tocopherols and carotenoids effectively inhibit photosensitised oxidation of vegetable oils. Direct gas chromatographic analyses of malonaldehyde do not correlate with the TBA test. Model fluorescence studies indicate that malonaldehyde may not be so important in crosslinking with DNA. In contrast to oxidised methyl linoleate, oxidised trilinolenin does not form dimers. Although trilinolein oxidises with no preference between the 1(3)-and 2-triglyceride positions, the n-3 double bond of trilinolenin oxidises more in the 1(3)- than in the 2-position. Synthetic triglycerides oxidise in the following decreasing relative rates: LnLnL, LnLLn, LLnL, LLLn (Ln = linolenic and L = linoleic). To estimate the flavour impact of volatile oxidation products their relative threshold values must be considered together with their relative concentration in a given fat.

Review. Recent advances in lipid oxidation

Based on experimental observations made in photosynthetic organisms which lacked colored carotenoid pigments, a hypothesis was developed that these pigments could serve as protective agents against photosensitized oxidations. Over the last 20 years, many workers have confirmed this hypothesis and have extended the observations to non-photosynthetic bacteria, plants and animals. It has also been possible to demonstrate carotenoid protection in in vitro systems. This article reviews the major mechanisms whereby carotenoid pigments protect cells against harmful photosensitized oxidations. The mechanisms include: (1) Carotenoid quenching of triplet sensitizers. (2) Carotenoid quenching of O2 (1δg). (3) Carotenoid inhibition of free radical reactions.

https://media.iupac.org/publications/pac/1979/pdf/5103x0649.pdf

Eiji Fujimori

Papers

Interactions of Chlorophyll in its Triplet State with Oxygen, Carotene, Etc.

Some Properties of the Ground Triplet State of Chlorophyll and Related Compounds1

Chlorophyll-photosensitized Reduction of Triphenyltetrazolium Chloride by Hydrazine Hydrate