Radicals phenothiazines

Common inhibitors include stable radicals (Section 5.3.1), oxygen (5.3.2), certain monomers (5.3.3), phenols (5.3.4), quinones (5.3.5), phenothiazine (5.3.6), nitro and nitroso-compounds (5.3.7) and certain transition metal salts (5.3.8). Some inhibition constants (kjkp) are provided in Table 5.6. Absolute rate constants (kj) for the reactions of these species with simple carbon-centered radicals arc summarized in Tabic 5.7. 

In contrast to phenols (Section 5,3.4), phenothiazine (39) is reported to be an excellent scavenger of both carbon-centered and oxygen-centered radicals by hydrogen atom transfer and is also used to stabilize monomers in storage.198... 

EGC > EC = C determined using artificial water-soluble phenothiazine radical cations (Salah et al., 1995) and EGCG > EGC > ECG > C determined in a mixture of LDL and VLDL. However, in the oxidation of unilamellar liposomes of phosphatidylcholine initiated with a water-soluble azo compound at 37°C, the antioxidant activities of EGCG and EGC were lower than those of EC and ECG at pH 7.4, and their depletion of EGCG and EGC was faster than that of EC and ECG (Terao et al, 1994). 

Magnetic Field Effects on the Dynamics of the Radical Pair in a Cgo Clusters-Phenothiazine System... 

MFEs on the dynamics of the radical pair in CtoN" clusters (C oN " ) -MePH system were examined in TH F-H2O (2 1) mixed solvent. M FEs on the decay profiles of the transient absorption at 5 20 nm due to the phenothiazine cation radical (P H " ) are shown in Eigure 15.9b. The decay was retarded in the presence of the magnetic field. In addition, the absorbance at 10 (is after laser excitation increased with increasing magnetic field. The result indicated that the yield of the escaped PH increased with the increase in magnetic field. Therefore, the MFEs on the decay profile were clearly observed. 

Keywords Pulse radiolysis Pyrene Phenothiazine Radical cation Hole transfer rate... 

One of numerous examples of LOX-catalyzed cooxidation reactions is the oxidation and demethylation of amino derivatives of aromatic compounds. Oxidation of such compounds as 4-aminobiphenyl, a component of tobacco smoke, phenothiazine tranquillizers, and others is supposed to be the origin of their damaging effects including reproductive toxicity. Thus, LOX-catalyzed cooxidation of phenothiazine derivatives with hydrogen peroxide resulted in the formation of cation radicals [40]. Soybean LOX and human term placenta LOX catalyzed the free radical-mediated cooxidation of 4-aminobiphenyl to toxic intermediates [41]. It has been suggested that demethylation of aminopyrine by soybean LOX is mediated by the cation radicals and neutral radicals [42]. Similarly, soybean and human term placenta LOXs catalyzed N-demethylation of phenothiazines [43] and derivatives of A,A-dimethylaniline [44] and the formation of glutathione conjugate from ethacrynic acid and p-aminophenol [45,46],... 

Hydroxychlorpromazine and chlorpromazine sulphoxide generated hydroxyl radicals when excited at 330 nm under either anaerobic or aerobic conditions. It is interesting that phenothiazine sulphoxides and 7-hydroxychlorpromazine have been associated with ocular opacity. It was suggested that the highly reactive hydroxyl radicals may be the cause of this. Chlorpromazine does not damage the eye [209]. 

Dixon and Mountain reported that exposure of mice to ozone at 1 ppm for 5 h resulted in a depletion of lung histamine content to as low as 75% of the control value 5 days later. They also observed that pretreatment with promethazine, an antihistaminic agent, resulted in a decrease in the amount of pulmonary edema produced by a sublethal dose of ozone. However, promethazine, in addition to being a potent antihistaminic agent, is a phenothiazine derivative and thus might act to trap fiee radicals or stabilize membranes. 

For the related compounds, phenothiazine and phenoxazine, the reduced form is stable under ambient conditions and oxidation occurs in two one-electron steps. A comparison between the redox behaviour of the two compounds is best made in an antimony trichloride medium where both the radical-cation and the dication levels are stable (Scheme 6.9) [225]. In perchloric acid, phenothiazine shows reversible... 

Preparative scale electrochemical oxidation of phenothiazine in aqueous acetonitrile, with no added acid, leads to the radical formed by proton loss from the radical-cation. The radical dimerizes and further oxidation leads to the green qui-nonoid cation 67 [230]. 

The advantage of using free radical inhibitors to facilitate the copolymerization of a bisbenzocyclobutene with a bismaleimide was first noted in a patent to Bartmann [78]. Subsequent to this, Corley in a series of patents described some detailed experiments on the copolymerization of bisbenzocyclobutenes with bismaleimides both with and without the addition of a free radical inhibitor [33, 34]. The structures of the bisbenzocyclobutenes used in this study are shown in Fig. 33. The bismaleimide component that was used was a mixture of three different bismaleimides in the molar ratio shown in Fig. 34. The individual bisbenzocyclobutenes were blended at elevated temperature with varying amounts of the bismaleimide composition. In some of the experiments, the free radical inhibitor phenothiazine was added at a 0.5 mole % level. The various monomer mixtures were then copolymerized using one of the cure schedules described in Table 14. The copolymers were then physically characterized using a variety of techniques. Table 14 shows the results obtained from copolymers... 

A number of nucleophilic molecules can lose electrons in enzyme-catalyzed reactions (e.g., peroxidase). Thus hydrazines, amines, hydroquinones, phenothiazines, thiols, and aminophenols can form free radicals by this mechanism. 

Various phenothiazines (176) have been oxidized in CH3CN-Et4NC104 to a stable radical-cation (R = OCH3). The free radical resulting from deprotonation of the radical-cation gives in those cases where R = H, SCN, or t-Bu a C—N bond dimer, possibly 177272,2-73 [Eq. (107)]. 

Phenoxazines and phenothiazines (446 X = 0, S) may be oxidized to phenoxazonium and phenothiazinium salts (447 X = 0, S). Radical cations are intermediates these lose H+ to form a neutral radical followed by another electron to form the six-rr-electron system (Scheme 53). On careful oxidation, radical cations (446a) can be isolated as deep-colored crystalline salts, stable enough for X-ray analysis (80JHC1053, 81JCS(P2)852, 88CB2059). 

Seven phenothiazines have been titrated with electrogenerated bromine in the range 0.1-3 mg with an average error of less than 1% [43]. The assay utilizes the oxidation of the phenothiazine in two one-electron steps to a cation-free radical and sulfoxide, respectively. 

Heterocyclic substrates in SET processes have been widely studied, including the reactions of diliydroiiicotiiiamide,116 pyridine, and quinoline117 and also phenoxazine and phenotiiiazines.118 Phenothiazine has also been shown by ESR analysis to undergo an electron-transfer reaction witii its radical cation with an appreciable 15N/14N isotope effect.119 The reaction of phenazine di-A -oxidc radical cations with hydrocarbons shows evidence of non-radical processes.120... 

Phenothiazine is readily oxidized when irradiated in solution with chlorinated hydrocarbones (8). The reaction has been shown to be an electron transfer generating the phenothiazine (PTH) radical cation (PTH+ ) and the halogen anion as shown in equation 1. hv. ... 

Other isolated products consist of the 3H-phenothiazine-3-one derivatives B (13), C and D ( 11), the formation of which may be explained by a radical hydroxylation of PT . 

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