Free radical, redox potential

This strategy was first realized by Lozinsky et al., who studied the redox-initiated free-radical copolymerization of thermosensitive N-vinylcaprolactam with hydrophilic N-vinylimidazole at different temperatures, as well as by Chi Wu and coworkers. Lozinsky presents an extensive review of the experimental approaches, both already described in the literature and potential new ones, to chemical synthesis of protein-like copolymers capable of forming core-shell nanostructures in a solution. 

The fates of the G(-H) radicals in DNA are mostly determined by reactions with other substrates. Here, we consider the reactions of the G(-H) radicals with types of free radicals that are generated in vivo under conditions of oxidative stress. One of these radicals is the nitrogen dioxide radical, NO2. This radical can be generated in vivo by the oxidation of nitrite, N02, a process that can be mediated by myeloperoxidase [111, 112] as well as by other cellular oxidants [113, 114]. An alternative pathway of the generation of NO2 is the homolysis of peroxynitrite [102, 115] or nitrosoperoxycarbonate formed by the reaction of peroxynitrite with carbon dioxide [99-101]. The redox potential, E°( NO2/NO2")=1.04 V vs NHE [116] is less than that of guanine, E7[G(-H)7G] = 1.29 V vs NHE [8]. Pulse radiolysis [117] and laser flash photolysis [109] experiments have shown that, in agreement with these redox potentials, N02 radicals do not react with intact DNA. However, N02 radicals can oxidize 8-oxo-dG that has a lower redox potential ( 7=0.74 vs NHE [56]) than any of the normal nucleobases [109]. 

Wardman P (1991) The reduction potential of benzyl viologen an important reference compound for oxidant/radical redox couples. Free Radical Res Comnun 14 57-67 Weeks JL, Rabani J (1966) The pulse radiolysis of deaerated aqueous carbonate solutions. I. Transient optical spectrum and mechanism. II. pKfor OH radicals. J Phys Chem 70 2100-2105 Yu X-Y, Barker JR (2003) Flydrogen peroxide photolysis in acidic solutions containing chloride ions. 

To investigate the importance, not only of laccase mediators, but also of lacca-ses per se, several laccases were studied for the oxidation of the nonphenolic lignin dimer I. In the presence of the redox mediators 1-HBT or violuric acid, it was found that the oxidation rates of dimer I by the laccases differed considerably. In oxidation of dimer I, both 1-HBT and violuric acid were to some extent, consumed. The consumption rate followed the same order of laccases as the oxidation rates of dimer I. The oxidation rate of dimer I was found to be dependent on both k, jt and the stability of the laccase in question. Both 1-HBT and violuric acid inactivated the laccases— violuric acid to a greater extent then 1-HBT. The presence of dimer I in the reaction mixture slowed down this inactivation. Inactivation seems to be mainly due to the reaction of the redox mediator free-radical with the laccases. No relationship between the carbohydrate content of the laccases and their inactivation was found. When the redox potential of the laccases is in the range of 750-800 mV, i.e., about that of the redox mediator, a further increase in redox potential does not affect k(,jt and the oxidation rate of dimer I [147]. 

P. Wardman, The reduction potential of benzyl viologen an important reference compound for oxidant/radical redox couples. Free Radical Res. Commun., 14 (1991) 57. 

Deactivation of the Mediator Deactivation of the mediator is a commonly encountered event in the practice of homogeneous catalysis. Among the various ways of deactivating the mediator, the version sketched in Scheme 2.10 is particularly important in view of its application to the determination of the redox characteristics of transient free radicals (see Section 2.7.2).14 The current-potential responses are governed by three dimensionless parameters, 2ei = /F)(ke Cjl/v), which measures the effect of the rate-determining... 

Both reacting intermediates, TPrA and Ru(bipy)33 + species, are produced simultaneously during electrochemical oxidation Actual ECL mechanism, however, is somewhat more complicated than expressed by the above reaction pattern with ECL emission from Ru(bipy)32+/TPrA system depending on the applied electrode potential. Usually, the direct oxidation of TPrA at the electrode occurs at more negative potentials than characteristic for the Ru(bipy)32+/Ru(bipy)33 + redox couple. Generally, the ECL emission from Ru(bipy)32+/TPrA system as a function of applied potential consists of two emission waves (both associated with the emission from 3 Ru(bipy)32 + ) attributed to TPrA and Ru(bipy)32 + oxidation, respectively.154 First emission wave corresponds to annihilation of sufficiently stable TPrA + (with half-life of 0.2 ms) and Ru(bipy)3 + species with Ru(bipy)3 + intermediate formed from the reduction of Ru(bipy)32+ by TPrA free radical ... 

Due to the variety of enzymatic environments in which FAD/ FADH /FADHZ can be held, enzymes that contain them exhibit redox potentials ranging from -0.45 to + 0.15 V at pH 7 (Bugg, 1997). Xenobiotic compounds whose structures suggest they can be reduced via free radical mechanisms or via hydride transfers may be reduced by such flavoproteins. 

---