Reduction , pulse-radiolytic

O Neill P, Chapman PW. (1985) Potential repair of free radical adducts of dGMP and dG by a series of reductants pulse radiolytic study. Int J Rad Biol 47 71-80. 

The physical and chemical properties of Rh(bpy)32+ generated via flash-photolytic and pulse-radiolytic methods in aqueous solutions are reported and discussed. The reduction potential -0.86 V vs SHE) and electron-exchange rate (> 109 M 1 s "1) for the Rh(bpy)33+/Rh(bpy)32+... 

Spectrophotometry has been a popular means of monitoring redox reactions, with increasing use being made of flow, pulse radiolytic and laser photolytic techniques. The majority of redox reactions, even those with involved stoichiometry, have seeond-order characteristics. There is also an important group of reactions in which first-order intramolecular electron transfer is involved. Less straightforward kinetics may arise with redox reactions that involve metal complex or radical intermediates, or multi-electron transfer, as in the reduction of Cr(VI) to Cr(III). Reactants with different equivalences as in the noncomplementary reaction... 

This oxidation state which resembles Cu(II) may be prepared by electrochemical, photochemicalor pulse radiolytic reduction of nickel(II). Nickel(I) macrocycles are powerful reductants and their spectra and redox potentials have been measured. The reactions of the Ni(I) complexes Ni(tmc) 10 and 11 with RX are similar. 

Halo-alkenes are common pollutants. Therefore, there is an ongoing study on plausible approaches to the dehalogenation of halo-alkanes. One of these approaches involves their electrocatalytic reduction. NinL2 + (L = a tetraaza macrocyclic ligand) complexes were proposed as plausible electrocatalysts (150). A pulse radiolytic study on the mechanism and kinetics of the reaction ... 

Reduction of the tetraoxomanganates Mn04, Mn04 , and Mn04 by pulse radiolytically-generated free organic radicals leads to the unstable [Mn 03(0H)] and [Mn 03(0H) ] species. They were characterized by their UV-visible spectra and their corresponding acid dissociation constants have been determined. ... 

Figure 2. Time-resolved absorption changes induced by reaction of pulse radiolytically produced C02 radicals with P. aeruginosa azurin. (a) Reduction of Cu(II) followed at 625 nm. (b). Formation and decay of the di sulfide radical anion measured at 410 nm. Protein concentration is 1 OpAf, where T = 298 K pH 7.0 0.1M formate 10 mM phosphate N2O saturated pulse width 0.4 ps optical path 12.3 cm. Time is in seconds the left panel shows the faster phase, while the right one shows the reaction taking place at the slower phase. The lower panels show the residuals of the calculated fits to the data.

Reacting the azurin dimer with pulse radiolytically produced C02 radical anions, the intermolecular disulfide bridge becomes reduced forming the RSSR radical in an essentially diffusion controlled reaction (fei 10 M s ). In contrast to the behavior of monomeric azurins, no competing bimolecular reduction of the blue Cu(Il) center by C02 was observed. Disulfide reduction was followed by concentration independent, intramolecular RSSR Cu ET (Fig. 5) ... 

Finally, it is of interest to compare intramolecular ET in hCp with the corresponding processes in laccase and ascorbate oxidase. As in hCp, pulse radiolytically produced RSSR radicals are also the primary reaction products in tree laccase (73), and the reduction equivalents are further transferred to the TFCu ) center in an intramolecular process. The rate of Tl(Cu ) reoxidation by intramolecular ET to T2/T3 takes place unimolecularly with a rate constant of 2s at room temperature, similar to that observed in hCp (2.9 s ), which is hardly surprising, since the stmctural arrangements of the T1-T2/3 sites in these two proteins are quite similar (the driving forces also are comparable). The situation in ascorbate oxidase, however, was found to be more complex (Section... 

Methylnicotinamide radicals (1-MNA ), produced pulse radiolytically, react with Ps-NiR concomitantly with the appearance of an absorption increase at 554 nm, a characteristic wavelength for heme-c reduction [Fig. 18(a)] (105, 106). At 670 nm, where heme-t/i reduction can be independently monitored, no absorption changes were observed in the fast time domain [Fig. 18(h)], indicating that no parallel bimolecular reduction of the heme-di center by 1-MNA is taking place. Therefore it was concluded that only heme-c is reduced directly by 1-MNA and in an essentially diffusion controlled process, with a second-order... 

Equilibrium Results During Full Pulse Radiolytic Reduction of cdi NiR" at 298 K... 

The steady state radiolysis of gold compounds is mainly concerned with the reduction of trivalent gold to the metal (13, 16). The reported yield, G(-Aum)eq = 2.3 0.2 (16), has been interpreted to arise from 2GH2o2 + Gh — G0h, where the G s stand for the primary radiolytic yields. From the point of view of pulse radiolytic investigation, Au1 is, however, more interesting. Since monovalent gold is unstable except when complexed (17), the choice of a suitable compound is very limited. 

Pulse radiolytic reductions were conducted without employing a hydrophilic host molecule. Radical-induced reduction of e-C6o[C(COO )2]2 in N2-purged aqueous solution showed that the expected formation of the diagnostic NIR transition band occurs synchronously with the decay of the electron absorption. The fullerene 7t-radical anion, absorbs at 1055 nm, which is 5 nm blue-shifted relative to the analogous reduced ester derivative. 

Qumones are capable of reacting with a large number of radiation-produced primary species like eaq, H and OH [14-16]. While eaq and H may reduce quinones by one-electron reduction process to the semiquinone, OH may either add to the ring or some suitable substituent position and give rise to one-electron oxidation to some form of transient. Formation of semiquinones by y-radiolysis has been discussed in detail m earlier monographs [7,9,17-19] and will not be included here. Pulse radiolysis kinetic spectrophotometry technique [20,21] has opened up new scope for detailed studies [8-12,15,16,22-25] on semiquinones. On pulse radiolytic one-electron reduction of quinones, semiquinones may be formed as follows -... 

P.C. Wilkins and R.G. Wilkins, Rapid Pulse Radiolytic Reduction of Iron(III) Complexes of Tetrakis(4-sulfonatophenyl)porphine Anion and Tetrakis(N-methylpyrid-4-yl)porphine Cation, Inorg. Chem., 25 (1986) 1908. 

Pulse radiolytic studies of the kinetics of formation of clusters containing two different metals are more readily accessible, for the reasons given above, when both ions may be reduced by a monoelectronic process. This can be achieved with mixed solutions of the monovalent ions Ag and Au, in the form of KAg(CN)2 and KAu(CN)2. " The evolution of the optical absorption spectrum with time was followed specifically at 400 and 520 nm, which correspond to the maxima of the surface plasmon bands of the monometallic silver and gold clusters, respectively. The early steps of the mechanism are rapid reductions of Ag and Au into atoms... 

In the current literature the pulse radiolytic oxidation-reduction cycle is prefered. As a consequence, a steady state level of 50 % reduced copper should be present during catalysis. Intriguingly, only 25 % of the copper was found to be reduced during steady state. Recently it was demonstrated, that the steady state level of oxidized copper is actually 50 % but can change to 75 % in previously lyophilized samples... 

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