Free-radical quenchers

Nihro, Y., Miyataka, H., Sudo, T., Matsumoto, H. and Satoh, T. (1991). 3-O-Alkylascorbic acids as free radical quenchers synthesis and inhibitory activity effect on lipid peroxidation. J. Med. Chem. 34, 2152-2157. 

A very important consideration in flammabilily is the presence of surfaces. Cold surfaces act as free-radical quenchers and maintain the gas temperature below the ignition temperature, while hot surfaces can act as ignitors. 

As antioxidants are free radical quenchers, the level of the added antioxidants in the refined oil decreases while the oil is in storage or in transit. However, one must recognize the fact that, because of the presence of antioxidants, the free radical content of the oil is going to be low at the time it is added to the fryer (provided the oil is not stored for too long or oxidized as a result of mishandling before use). 

Synovial fluids (SF) are highly viscous liquids that contain rather high amounts of high-molar-mass HA (normally about 2-3 mg/ml). Due to their profound biological significance, SF have been comprehensively studied. For instance, y-irradiation of SF results in a dose-dependent degradation of HA [71, 72]. This effect can be effectively suppressed by common free radical quenchers such as N-acetyl-L-cysteine [108] and is, thus, mediated by ROS, not by enzymes. 

AUcylascorbic acids acted as free radical quenchers and, dependent upon their hydrophobic-ity, inhibited Fe -ADP-induced lipid peroxidation (Nihro et al. 1991). HX-0112 and HX-0113, which are stable lipophilic ascorbic acid derivatives, alleviated myocardial lesions induced by ischaemia-reperfusion treatment in rats (Sasamori et al.). 

Carotenoids, in particular P-carotene, are well-known free-radical quenchers [78]. It has been shown that peroxy radicals can oxidise P-carotene to the corresponding radical cations [78]. Absorption spectra demonstrate the appearance of broad bands in the range 600-1000 nm with = 910 nm (e = 9.4 x lOVM/cm) during pulse radiolysis of solutions of P-carotene in tert-butyl alcohol - water mixtures containing nitrate [79]. These bands were attributed to P-carotene radical cations generated by electron abstraction from the substrate by NO radicals ... 

See Free-radical scavengers, Peroxide decomposers, Quenchers, Ultraviolet absorbers, Ultraviolet screening agents. 

In most cases two different additives are used, one acting as an internal filter or excited state quencher and the other one being a scavenger of free radicals. These two additives have a synergic effect, that is they are much more effective together than either of them separately. 

These molecules have no absorption in the near UV, so they cannot act as internal filters. There is no evidence that they could act as quenchers of the excited impurity chromophores in common polymers, and it has been mentioned already that such quenching action would be, in any case, unlikely to be important in relatively rigid systems such as polymers. This remark does not apply to free radical scavengers, because a free radical has an unlimited lifetime since it can disappear only through a chemical reaction with another open-shell molecule. 

Light Stabilizers Pigments (carbon black, iron oxides), UV absorbers (hydroxyphenones, benzotriazoles), excited-state quenchers (organic Ni complexes), free-radical scavengers Hindered amine light stabilizers [piperidines, hindered amine light stabilizers (HALS)]... 

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