Light Emission Resulting from Hydroxylamine‐Induced Singlet Oxygen Formation of Oxidizing LDL Particles

Abstract

Oxidation of low-density lipoprotein (LDL) by low amounts of cupric ions resulted in the formation of singlet oxygen (1O2, 1 delta g) when hydroxylamine (NH2OH) was added. Direct evidence on this excited species came from partial spectral resolution of the emitted light in the red spectral region (634 nm and 703 nm), which can be attributed to the dimol decay of singlet oxygen. Additional evidence for the existence of singlet oxygen came from the enhancing effect of deuterium oxide buffer (D2O) on chemiluminescence intensity and the quenching effect of sodium azide. A linear correlation between NH2OH-dependent chemiluminescence intensity and the amount of diene conjugates (DC) formed in this reaction was observed. Removal of adventitious transition metals by adequate chelators prevented chemiluminescence in this system; NH2OH was also found to efficiently decrease metabolites of lipid peroxidation (LPO). Our findings are consistent with a sequence of reactions in which NH2OH first converts transition metals to their reduced state, thereby stimulating the formation of alkoxy- and peroxyradicals. Peroxyradicals decompose in a bimolecular Russel reaction to hydroxyl compounds and singlet oxygen while the majority of alkoxy radicals are eliminated by a secondary reaction with NH2OH. Identical effects were observed when reducing antioxidants such as ascorbic acid or trolox C were used instead of hydroxylamine.

TiO2-Assisted Photodegradation of Dyes. 9. Photooxidation of a Squarylium Cyanine Dye in Aqueous Dispersions under Visible Light Irradiation

“…By contrast, alkoxy (RO • ) or alkyl (R • ) radicals formed from the reaction of the organoperoxide ROOH with Fe 3+ species (eqs 10−13) produce DMPO- • OR, DMPO- • OOR, or DMPO- • R adducts with DMPO all of which typically display a six-line ESR spectrum for the oxygen-centered and carbon-centered radical in the aqueous system. , RH represents the organic compound. Accordingly, the aqueous dispersion irradiated for different time intervals by visible light (halogen lamp) was sampled, and then DMPO and Fe 3+ were added to probe the organoperoxy radicals by the spin-trap ESR technique.…”

Photoassisted Degradation of Dye Pollutants. 8. Irreversible Degradation of Alizarin Red under Visible Light Radiation in Air-Equilibrated Aqueous TiO2 Dispersions

“…An organoperoxide can cleave and produce organic radicals by reaction with Fe 3+ as noted in reactions 1−3 (): These organic radicals (ROO • , RO • , R • ) can be trapped by DMPO and produce the corresponding ESR signals of DMPO− • OR or DMPO− • R and/or DMPO− • OOR adducts ( , ). We detected no characteristic ESR signals for any of these radical adducts in the system under otherwise identical conditions as above.…”

Photooxidative Damage of Guanine in DG and DNA by the Radicals Derived from the α Cleavage of the Electronically Excited Carbonyl Products Generated in the Thermolysis of Alkoxymethyl-Substituted Dioxetanes and the Photolysis of Alkoxyacetones

“…As for the origin of these oxidants, they are formed during oxygen metabolism or by exposure to UV radiation (sunlight). The latter involves electronically excited states, which may be generated by excitation of endogenous sensitizers, but also by lipid peroxidation (Russell mechanism) …”