Oxygen peroxide species

It is well established that aerobes constantly produce small amounts of oxygen-derived species, such as the superoxide radical (02 ), hydrogen peroxide (H2O2) and hypochlorous acid (HOCl), the latter being generated by... 

It is possible that steric factors prevent the formation of the bridging peroxide species in the case of vitamin Bj2,. (55), however, other cases have been reported (59) in which oxygenation proceeds no further than the formation of mononuclear peroxo radicals (i.e. first stage above). 

Different mechanisms to explain the disinfection ability of photocatalysts have been proposed [136]. One of the first studies of Escherichia coli inactivation by photocatalytic Ti02 action suggested the lipid peroxidation reaction as the mechanism of bacterial death [137]. A recent study indicated that both degradation of formaldehyde and inactivation of E. coli depended on the amount of reactive oxygen species formed under irradiation [138]. The action with which viruses and bacteria are inactivated by Ti02 photocatalysts seems to involve various species, namely free hydroxyl radicals in the bulk solution for the former and free and surface-bound hydroxyl radicals and other oxygen reactive species for the latter [139]. Different factors were taken into account in a study of E. coli inactivation in addition to the presence of the photocatalyst treatment with H202, which enhanced the inactivation... 

The extreme hazards involved in handling this highly reactive material are stressed. Freshly distilled material rapidly polymerises at ambient temperature to produce a gel and then a hard resin. These products can neither be distilled nor manipulated without explosions ranging from rapid decomposition to violent detonation. The hydrocarbon should be stored in the mixture with catalyst used to prepare it, and distilled out as required [1], The dangerously explosive gel is a peroxidic species not formed in absence of air, when some l,2-di(3-buten-l-ynyl)cyclobutane is produced by polymerisation [2], The dienyne reacts readily with atmospheric oxygen, forming an explosively unstable polymeric peroxide. Equipment used with it should be rinsed with a dilute solution of a polymerisation inhibitor to prevent formation of unstable residual films. Adequate shielding of operations is essential [3],... 

The cytotoxicity of BLM is believed to result from its ability to bind iron, activate oxygen, and form an activated BLM (Fe-114) (556) which cleaves DNA and possibly RNA (557). The ability of the Fe(II)-BLM complex to bind to oxygen and produce oxygenated BLM species such as 02-Fe(III)-BLM or 02-Fe(II)-BLM may be due to the presence of delocalized 77-electrons around the iron and the strong iron-pyrimidine 77-back-bonding (558, 559). Oxygenated BLM accepts an additional electron to form activated low-spin ferric-peroxide-BLM (Oi -Fe(III)-BLM) (558, 559). The structural features of Fe-BLM responsible for DNA (or RNA) degradation remain unclear (560). Bleo-... 

According to the authors, the importance of the various reactions in this scheme depends on the catalyst properties, particularly the possibility of reaction between the allyl radical (complex) and lattice oxygen and the possibility of desorption of an allyl peroxide species. 

Schultes and Teil expressed the idea that oxygen was not really chemically adsorbed in the conventional sense, but might instead be bound in a manner intermediate between true chemical adsorption and physioftl adsorption. In other words, the oxygon on the silver surface might still be partially diatomic. Reaction with ethylene was then pictured as a completing to form a transient peroxide species C2H4O2, which could have one of two structures (Eq. 102), and which would react further very quickly, cither on the surface or after desorption. The intermediacy of this peroxide was unfortunately not established experimentally, however. 

The reaction of oxygen with cobalt(n) chloride and triphenylphosphine (L) in allylamine (AA) proceeds226 as shown in Scheme 4 [A] is probably a mixture of peroxidic species which dissolves on addition of BTH and precipitates an orange solid on irradiation. The same novel complex (48) is slowly deposited when solution [B] is allowed to stand in the dark oxidation of the PPh3 to OPPh3 has occurred under mild conditions. 

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