Peroxy radicals scavenger

Aromatic Amines. Antioxidants derived from -phenylenediarnine and diphenylamine are highly effective peroxy radical scavengers. They are more effective than phenoHc antioxidants for the stabilization of easily oxidized organic materials, such as unsaturated elastomers. Because of their intense staining effect, derivatives of -phenylenediamine are used primarily for elastomers containing carbon black (qv). 

The effectiveness of the UV absorbers may not be completely explained in terms of tautomerism. Among other mechanisms that have been proposed are energy transfer, involving an excited triplet state of the polymer (B-79MI11506), and peroxy radical scavenging, involving the formation of stable cyclohexadienones (78MI11502). 

We will not go in depth into the subject of antioxidants (12), which is more a part of preformulation than a stress test, but the autoxidation mechanism does suggest that oxidation can be inhibited by peroxy radical scavengers (chain-breaking antioxidants) like phenol antioxidants, by heavy metal chelating agents, and by peroxide inactivating substances (preventive antioxidants). 

Major flaxseed sterols are stigmasterol, camp sterol, and 5-5 avenasterol (Daun et al., 2003). Obtusifoliol, gramisterol, and citrostadienol constituted 45%, 22%, and 12%, respectively, of the total 4a-monomethylsterol in flaxseed (Kamm et al., 2001). Squalene content of flaxseed oil was reported as 4 mg/100 g oil, which was significantly lower than olive, corn, and rice bran oils. Squalene content is an intermediate compound of biosynthesis of plant sterols, which may have protective effects on lipid quality. Squalene could act as a peroxy radical scavengers in high polyunsaturated fatty acid oil (Dessi et al., 2002). 

Peroxyoxalates, as oxidants 1255, 1257, 1259 Peroxy radical scavenging 992 Pervaporation 983, 984 Perylenequinones, chemical shifts for, isotope effects on 345 Pesticides,... 

According to Reaction sequence (4.35), one diphenylamine molecule eliminates four peroxy radicals and, by definition, the stoichiometric factor is 4. For a steri-cally hindered monophenol, this factor is 2. Hence diphenylamines perform better as peroxy radical scavengers than do monophenols at temperatures <120°C. Under... 

Overbased phenates and salicylates Both phenates and salicylates of magnesium or calcium behave as antioxidants at high temperatures. The antioxidant activity may be related to hydroperoxide decomposition by the sulphur in structure XVIII and peroxy radical scavenging by the OH group in structure XIX [71]. Addition of MCO3 to phenates and salicylates leads to the corresponding overbased products, which also act as acid scavengers. 

The effectiveness of one class of antioxidant may be enhanced by combining it with another type of stabiliser. Hence, combining two different peroxy radical scavengers in a lubricant gives improved oxidation stability compared with either alone. This form of additive response is called synergism or, more specifically, homosynergism because they operate by the same stabilisation mechanism. The mechanism of this synergism is outlined as Reaction sequence (4.70) [74] ... 

Figure 3 shows the CL - time profile for samples of PP containing different concentrations of the profluorescent nitroxide TMDBIO. The CL curve for unstabilized PP shows that after a very short time, there is an exponential increase in CL corresponding to rapid oxidation and embrittlement of the polymer. The effect of the added nitroxide is not to decrease totally the CL from the PP, but rather to retard the emission so that there is a slower development of the CL emission intensity. There is thus an increase in the time taken to see the exponential increase in emission intensity, but the emission is not reduced to zero in this retardation period. In contrast, if a peroxy-radical scavenging, hindered phenol such as Irganox 1010 were to be added to the PP then the increase with time of the CL intensity would be totally suppressed and there would be an apparent induction period 8), This result may be interpreted within the framework of the free-radical reactions in Figures 1 and 2 above. 

In investigations of the antioxidant activity of phycocyanin with or without in vitro digestion, peroxy radical scavenging capacity of phycocyanobilin was 2.7-fold greater than that of the native protein (unpublished data). This result coincided with observations of increased peroxy radical scavenging of free phycocyanobilin or trypsin-digested phycocyanin, relative to native phycocyanin [49,50]. 

Rigo, A., Vianello, F., Clementi, G. (2000). Contribution of proanthocyanidins to the peroxy radical scavenging capacity of some Italian red wines. Journal of Agricultural and Food Chemistry, 48, 1996-2002. 

---