Nitroxyl radical, interaction

The resulting products, such as sulfenic acid or sulfur dioxide, are reactive and induce an acid-catalyzed breakdown of hydroperoxides. The important role of intermediate molecular sulfur has been reported [68-72]. Zinc (or other metal) forms a precipitate composed of ZnO and ZnS04. The decomposition of ROOH by dialkyl thiophosphates is an autocata-lytic process. The interaction of ROOH with zinc dialkyl thiophosphate gives rise to free radicals, due to which this reaction accelerates oxidation of hydrocarbons, excites CL during oxidation of ethylbenzene, and intensifies the consumption of acceptors, e.g., stable nitroxyl radicals [68], The induction period is often absent because of the rapid formation of intermediates, and the kinetics of decomposition is described by a simple bimolecular kinetic equation... 

Interaction of pyrroline-iV-oxides (373) with alkynylmagnesium bromide gives alkyne substituted nitroxyl radicals (374), (376), and (377) (Scheme 2.164) (620). 

Spin traps. Nitroso compounds and nitrons (A-oxides) interact with radicals to form nitroxyl radicals (Scheme 4.22). 

To obtain semiconductors with magnetic properties, Fujiwara et al. (2003) developed several donor molecules containing a stable oxyl radical moiety based on the n-extended TTF framework. The TTF framework is too small to overcome the steric hindrance of the bulky nitroxyl radical and to accomplish strong intermolecular interaction indispensable for any electric conductivity. For this reason, a larger molecule was constructed and its cation-radical perchlorate was electrochemically prepared. This salt was obtained as black microcrystals of nonstoichiomteric ratio equal to 1 0.64. Being a semiconductor, the salt also manifests magnetic properties its structure is depicted in Scheme 8.13. 

Analysis of reaction rate constants in model systems shows that at room temperature, the main reaction leading to regeneration of nitroxyl radicals is their interaction with peroxide radicals, (Reaction 11) and at elevated temperatures (more than 80°) the main reaction is that of hydroxylamine ether decomposition (Reaction 15) (53). 

Adhesion. A promising trend in nitroxyl radical application is associated with the modification of polymer surfaces to promote adhesion. Bonds which are formed as a result of the interaction of radicals with a surface and an adhesive are known to be of great importance for the forces determining the adhesion of the system. 

Elimination of the yellowing introduced by the stable nitroxyl radicals was essential for commercial development of these excellent stabilizers. Since phenolic antioxidants are necessary for the thermal stabilization of polymers during processing, we turned our attention to ways in which unfavorable interactions between the hindered phenols and the stabilizing nitroxyl radicals could be avoided. In this section we describe the discovery of the light-stabilizing activity of hindered amine compounds, an improved synthetic method for these compounds, the synthesis of a number of derivatives, and the evaluation of their stabilizing activity. 

DNA base radicals induced by OH radicals are also a possible target for interactions with nitro-aromatics [117]. For instance, the OH adducts of the nucleobases with reducing properties interact with nitro-aromatics to form nitroxyl adducts [118]. The rate constants for this interaction show only a weak dependence on the one electron reduction potential of the nitro-aromatic. However, using poly C as a model for a biopolymer, the nitroxyl radical adducts formed through addition of nitrofurantoin to the C-6 position of the C(5)-OH... 

The mechanism of ssb enhancement and radiosensitisation may be related in some way to those oxidants which form adducts with the DNA radicals. With the nitroaromatics a plausible enhancement of ssb is the possible H-atom abstraction by the base nitroxyl radical. The reactivity of the nitroxyl adducts with thiols or other reductants has not been studied in detail as there are at least two possible interactions where competition between the nitro-aromatic and a thiol may occur as shown in reactions (11-15). 

Figure 52 Models of substrate-catalyst interaction, (a) Energy-minimized structure of substrate 1-phenylethanol docked in the cleft of peptoid 141 as viewed perpendicular to the helix axis (Left) and down the helix axis with the N-terminus projecting forward (Right), (b) The substrate 1-phenylethanol approaching the catalytic TEMPO site of the sterically encumbered scaffold of peptoid 143. The ovals represent the reaction site comprising the snbslrate hydroxyl group and TEMPO nitroxyl radical. Color key hy ogen, white oxygen, red nitrogen, blue 1-phenylethanol (substrate), green. (Reprinted with permission from Ref. 190. National Academy of Sciences of the United States, 2009.)...

INTERACTION OF STABLE NITROXYL RADICALS WITH RADIATION-INDUCED SPECIES A PULSE RADIOLYTIC STUDY... 

As can be seen, the hydroperoxide consumption rate is initially low and then sharply increases. The observed character of the kinetic curves cannot be explained by reactions (74) or (75). According to the ESR data, the decomposition of PP hydroperoxide in an NO atmosphere gives dialkylnitroxyl radicals. It was shown that the induction periods for the hydroperoxide decomposition and nitroxyl radical accumulation are very sensitive to the presence of trace amounts of higher nitrogen oxides. This leads to the conclusion that the interaction of hydroperoxide with NO is more likely to proceed according to the scheme ... 

As stabilisers are often used in combination interactions are possible. ESR studies in the liquid state have been used to elucidate such interactions, e.g. with HALS/phenol mixtures it is possible to obtain information about the interactions between nitroxyl radicals and phenols, nitroxide radicals and phenoxy radicals, between phosphites, nitroxyl and phenoxy radicals in phosphite/phenol and phosphite/HALS mixtures. The results are useful for optimisation of additive formulations. 

At amorphous glassy polymers as natural nanocomposites treatment the estimation of filling degree or nanoclusters relative fraction (p j has an important significance. Therefore, the authors of Ref. [27] carried out the comparison of the indicated parameter estimation different methods, one of which is EPR-spectroscopy (the method of spin probes). The indicated method allows to study amorphous polymer structural heterogeneity, using radicals distribution character. As it is known [28], the method, based on the parameter - the ratio of spectrum extreme components total intensity to central component intensity-measurement is the simplest and most suitable method of nitroxyl radicals local concentrations determination. The value of dipole-dipole interaction is directly proportional to spin probes concentration C [29] ... 

This EPR spectrum shows a considerable broadening of linewidth when comparing with an EPR spectrum of free TAM nitric oxide. An EPR characterization of nitroxyl radicals is based on the measurement of the signal intensity of an EPR spectrum. This measurement can provide fundamental information of free radicals, such as linewidth that bears a relationship to the tumbling motion of free radicals, g-value which largely depends on the immediate environments of the free radicals, and hyperfine splitting constants which describe the classical multiplicity of EPR spectrum due to the interaction of the unpaired electron spins with nuclear spins. 

Thus, the interaction of 3-imidazoline derivatives and 3-imidazolinium salts with electrophilic reagents makes it possible to obtain various derivatives of this series, containing a nitroxyl radical center. 

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