The evolution of angiosperm plants between 50 and 200 million years ago resulted in the development of many antioxidant pigments – particularly during the Jurassic period – as chemical defences against reactive oxygen species that are byproducts of photosynthesis.

Research into how vitamin E prevents the process of lipid peroxidation led to the identification of antioxidants as reducing agents that prevent oxidative reactions, often by scavenging reactive oxygen species before they can damage cells.

A paradox in metabolism is that, while the vast majority of complex life on Earth requires oxygen for its existence, oxygen is a highly reactive molecule that damages living organisms by producing reactive oxygen species.

However, reactive oxygen species also have useful cellular functions, such as redox signaling.

The use of oxygen as part of the process for generating metabolic energy produces reactive oxygen species.

In plants, algae, and cyanobacteria, reactive oxygen species are also produced during photosynthesis, particularly under conditions of high light intensity.

This effect is partly offset by the involvement of carotenoids in photoinhibition, and in algae and cyanobacteria, by large amount of iodide and selenium, which involves these antioxidants reacting with over-reduced forms of the photosynthetic reaction centres to prevent the production of reactive oxygen species.

The amount of protection provided by any one antioxidant will also depend on its concentration, its reactivity towards the particular reactive oxygen species being considered, and the status of the antioxidants with which it interacts.

There is also some limited evidence that some reactive oxygen species are created by visible light in skin, and that these may have some role in photoaging, in the same manner as ultraviolet A does.

DNA is also indirectly damaged by reactive oxygen species produced by ultraviolet A, which has energy too low to damage DNA directly.

Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen and water.

" When bacteria or other microbes are engulfed by phagocytes, the enzyme NADPH oxidase assembles in the membrane and begins to produce reactive oxygen species ( ROS ) that help kill bacteria.

This process is efficient, but a small percentage of electrons may prematurely reduce oxygen, forming reactive oxygen species such as superoxide.

Mutagenesis may occur endogenously, for example through spontaneous hydrolysis, or through normal cellular processes that can generate reactive oxygen species and DNA adducts, or through error in replication and repair.

Many compounds, such as PAHs, aromatic amines, aflatoxin and pyrrolizidine alkaloids, may form reactive oxygen species catalyzed by cytochrome P450.

Ionizing radiations and reactive oxygen species often oxidize guanine to produce 8-oxoguanine.

In general, antioxidant systems either prevent these reactive species from being formed, or remove them before they can damage vital components of the cell.

The term unstable molecule is used for very reactive species, i. e., short-lived assemblies ( resonances ) of electrons and nuclei, such as radicals, molecular ions, Rydberg molecules, transition states, van der Waals complexes, or systems of colliding atoms as in Bose-Einstein condensate

The metabolic process was identified in 1960s as catalysis by cytochrome P450 which produces reactive species that can interact with the DNA to form adducts, the mechanism by which the PAH adducts give rise to mutation however is still under investigation.

DNA may sustain more than 50, 000 damages per cell per day, and some estimates put the number of oxidative adducts per cell generated through reactive reactive oxidative species at 150, 000.

Oxidative stress may also generate highly reactive oxygen species that can damage the DNA.

Incorrect repair of other damages induced by the highly reactive species can also lead to mutations.

These chemicals are known to down-regulate the formation of reactive oxygen species, key chemicals in cardiovascular disease.

Catalysts may affect the reaction environment favorably, or bind to the reagents to polarize bonds, e. g. acid catalysts for reactions of carbonyl compounds, or form specific intermediates that are not produced naturally, such as osmate esters in osmium tetroxide-catalyzed dihydroxylation of alkenes, or cause lysis of reagents to reactive forms, such as atomic hydrogen in catalytic hydrogenation.

Construction of a high temperature proton exchange membrane fuel cell | PEMFC: Bipolar plate as electrode with in-milled gas channel structure, fabricated from conductive composite material | composite s ( enhanced with graphite, carbon black, carbon fiber, and / or carbon nanotube s for more conductivity ); Porous carbon papers ; reactive layer, usually on the polymer membrane applied ; polymer membrane. Condensation of water produced by a PEMFC on the air channel wall.

The free element ( metal ) is not found naturally on Earth, as it is highly reactive ( though once produced, it is coated in a thin layer of oxide ( see passivation ), which partly masks this reactivity ).

In electric power transmission, the characteristic impedance of a transmission line is expressed in terms of the surge impedance loading ( SIL ), or natural loading, being the power loading at which reactive power is neither produced nor absorbed:

As a result, reactive oxygen species are produced and oxidation reactions in excess of those normally tolerated by the cell occur, leading to plant death.

It has an antioxidant action that helps the microbe evade death by reactive oxygen species that are produced by the host immune system.

* reactive oxygen species such as superoxide, peroxide, and hypobromite ( hypobromous acid, which is preferentially produced by eosinophil peroxidase ).

Industrially, NaK is produced in a reactive distillation.

Additionally during the metabolism of MMH, N-methyl-N-formylhydrazine is produced ; this then undergoes cytochrome p450 regulated oxidative metabolism which via reactive nitrosamide intermediates leads to formation of methyl radicals which lead to liver necrosis.

The excess uroporphyrinogen that lead to these lesions is primarily produced in the liver, but exposure to excess sunlight is thought to lead to the production of reactive oxygen species, disrupting the activity of uroporphyrinogen decarboxylase and contributing to the buildup of uroporphyrinogen.

Additionally during the metabolism of MMH, N-methyl-N-formylhydrazine is produced ; this then undergoes cytochrome P450 regulated oxidative metabolism which via reactive nitrosamide intermediates leads to formation of methyl radicals which lead to liver necrosis.

In addition to energy, reactive oxygen species ( ROS ) with the potential to cause cellular damage are produced.

Excessive nitric oxide produced during reperfusion reacts with superoxide to produce the potent reactive species peroxynitrite.

# endogenous damage such as attack by reactive oxygen species produced from normal metabolic byproducts ( spontaneous mutation ), especially the process of oxidative deamination

Then in 1993, Nu-Line Industries produced the X-Calibur, a reactive resin cover.

There also is the possibility to have more than two reactive sites on a monomer: In this case branched polymers are produced.

New locally produced gun, new targeting systems, Detroit Diesel 8V-71T diesel engine, reactive armor.

NO < sub > y </ sub > ( reactive, odd nitrogen ) is defined as the sum of NO < sub > x </ sub > plus the compounds produced from the oxidation of NO < sub > x </ sub > which include nitric acid.