Pulse radiolysis experiments

Reactions such as these are of interest in themselves. Beyond that, one can use the pulse radiolysis experiment as a preparative technique for other species. Thus, the reactions of numerous aliphatic, carbon-centered radicals have been evaluated.22 If one employs a reasonably high concentration of solute, say 0.1-1 M CH3OH, the formation of CH2OH is complete within the electron pulse. Following that, reactions such as the following can be studied ... 

The product CO3 radical can react with a variety of inorganic ions including the carbonato complex of Pu(V). Thus, in a pulse radiolysis experiment, Pu(VI) in 0.05 M Na2C03, He saturated, there are the parallel reactions (17) and (18)... 

As seen before, the radical cation of dimethyl sulfoxide (0113)280 7 has been detected by E8R spectroscopy among other radicals when DM80 glasses at 77 K are submitted to y-irradiation . It has also been reported in pulse radiolysis experiments (Table 6). Constant current electrochemical oxidation of bis(dialkylamino)sulfoxides (R2N)280 gives rise to radical cations which have been detected by E8R spectroscopy . ... 

Laser flash experiments were also carried out with Q-CdS sols, in which the emission of hydrated electrons was observed The quantum yield was significantly greater than in similar experiments with larger particles of yellow CdS (Sect. 3.7). The electron emission was attributed to the interaction of two excitonic states in a particle produced during the flash CdS(e — h >2 CdS(h" ) + e q. The emitted electrons disappeared after the laser flash within 10 ps. After this time a long-lived absorption remained which was identical with the above-mentioned absorption of holes produced by OH radicals in the pulse radiolysis experiment. 

By employing an extinction coefficient for the anion radical obtained from the pulse radiolysis experiments, the concentration of the radical could be calculated, and plotted against /c. The straight line plot so obtained was taken as strong evidence for the ECE mechanism, i.e. the solution phase attack of C02 on C02, thus fully resolving the controversy over the identity and state of the intermediate. From the slope of the plot the authors obtained the rate constant k2 as 7.5 x I03dm3mol 1 s 1. 

Rate Constants for Reaction of Superoxide with Flavonoids and Related Compounds (Pulse-Radiolysis Experiments)... 

DR. CREUTZ Not yet. I don t believe that can be done in quite the same way. You will notice that none of the reactions we used to reduce Rh(III) involved homogeneous reducing agents that is because we have not found any which work. We anticipate difficulties with Rh(I) oxidation as well. Obviously, one would need conditions where oxidation of the Rh(I) to Rh(II) is more rapid than oxidation of the desired Rh(II). In pulse radiolysis experiments it might be possible to exploit oxidants such as (SCN) or Br. But we haven t yet attempted such experiments. 

The spectrum in the Soret region, indicative of the c-type center of the enzyme, immediately following the reduction is not identical to that obtained when the enzyme is fully reduced under steady-state/equilibrium conditions. This suggests that the reduced c-type cytochrome center formed under the conditions of the pulse radiolysis experiment retained the His/His coordination. 

The speed of the reduction by the solution radical generated in the pulse radiolysis experiment is also consistent with this proposal conformational rearrangements are highly unlikely on the microsecond time scale. 

The midpoint redox potential of a His/His coordinated heme is likely to be less than -l-lOO mV. Given that the d heme is catalyzing a reaction with a midpoint potential of approximately -1-350 mV, it can be expected to have a potential considerably more positive than -l-lOO mV. This would account for the stoichiometric transfer of electrons from the c heme to the di heme under the conditions of the pulse radiolysis experiment. 

Dajka, K Takacs, E Solpan, D Wojnarovits, L Guven, O. High-energy irradiation treatment of aqueous solutions of C.l. Reactive Black 5 azo dye pulse radiolysis experiments. Radiation Physics and Chemistry, 2003 67, 535-538. 

Pulse-radiolysis experiments allow an examination of the first steps in the decay of radical-cations. Solutions of the radical-cation in the region of 10 M are generated. Bimolecular reactions between species at this level of concentration proceed relatively slowly and this simplifies interpretation of the experimental data. Particularly, electron transfer between radical-cations and radical species derived from them is not observed during the experiment. 

The Jencks clock, as well as pulse radiolysis experiments, indicate that oxocarbenium cations often can be quite stabilized, with a half-life on the order of milliseconds. For example, at room temperature, the structures shown here (left to right) have respective lifetimes of... 

Pulse radiolysis experiments have shown that "OH radical adds preferentially at C5 of the uracil moiety, giving rise to the reducing 5-hydroxy-5,6-uracil-6-yl radical. Interestingly, the two cis diastereomers of 6-hydroperoxy-5-hydroxy-5,6-dihydrouridine, two of the expected final products of the latter radicals in aerated aqueous solutions, have been prepared by trifluoroacetic acid treatment of uridine (3, R = H, = ribose) in the presence of H202 (equation 14). The mechanism of the reaction that involves transient formation of an epoxide-type intermediate followed by nucleophilic attack by a perhy-droxyl group at C6 presents similarities with the substitution of thymine bromohydrin by... 

The first picosecond pulse radiolysis experiment was carried out in the late 1960s by the so-called stroboscopic method (generally pomp and probe method) at University of... 

Figure 6 Comparison of experimental and predicted values of G(Pi) from electron scavenging as a function of the scavenger power fcio[Si]. Si = N2O ( ) CH3CI (A) C(N02)4 ( ) glycylglycine ( ) NO3" (O). The broken line is predicted from direct observation of the time dependence of G e ) in pulse radiolysis experiments. (From Ref. 49.) The solid line is the fit obtained by Pimblott and LaVerne [43] with the restriction that G°(e q) = 4.80 molecules (100 eV) ...

The first pulse radiolysis experiments to measure G°(e ) directly were made in the 1970s, with reported values of 4.0 0.2 molecules (100 eV) at 30 psec [45] and 4.1 0.1 molecules (100 eV) at > 200 psec [46]. The latter value was subsequently revised to 4.6 0.2 molecules (100 eV) at 100 psec [47], and later a yield of 4.8 0.3 molecules (100 eV) at 30 psec was reported by Sumiyoshi et al. [48]. The method of evaluating G(e ) at these short times is either to use dosimetry [45,46] and the molar absorption coefficient of e, or to compare the optical absorbance at short times with that observed at 10 -10 sec and take G(e q) = 2.7 molecules (100 eV) at this time [48]. The causes of the discrepancies between these pulse radiolysis values have been reviewed recently by Bartels et al. [49], who have also made new measurements of the spur decay of e. ... 

In their pulse radiolysis experiments, Bartels et al. [49] measured directly the decay of e q from 100 psec out to microseconds. By using the four exponential sum in Eq. (21) to fit the observed decay, they obtained a ratio G°(0)/G nf of 1.59, effectively equivalent to G°(eaq)/ (eaq) ... 

HO2 and 02 have characteristic absorption spectra with s ax 140 mol at 225 nm [83] and Smav = 189 mol at 245 nm [85], respectively, which are sufficiently intense to permit their reactions to be followed by direct observation in pulse radiolysis experiments. Both radicals are relatively unreactive with organic molecules [83], abstracting only weakly bonded hydrogen atoms in, for example, ascorbic acid, cysteine, and hydroquinone. Oj undergoes reversible electron transfer in its reaction with quinones (Q), which was used to establish its reduction potential [86] ... 

The outer-sphere one-electron reduction of CO2 leads to the formation of the 02 radical anion. In dry dimethylformamide, the C02/ C02 couple has been experimentally determined to be —2.21 V vs. standard calomel electrode (SCE) or approximately —2.6 V vs. the ferrocene/ferrocenium couple [21,22]. From pulse radiolysis experiments, the reduction potential of CO2 is —1.90 V vs. the SHE in water (—2.14 V vs. SCE) [23]. Theoretical calculations have been used to calculate the contributions of various factors to the reduction potential of CO2. These include the electron affinity of CO2,... 

The author is indebted to the Argonne National Laboratory, Chemistry Division, and especially to J. K. Thomas, who performed the pulse radiolysis experiments and whose helpful suggestions made that part of... 

In pulse radiolysis experiments these radicals are formed by a short pulse, 10-12-10-6 s depending on the experimental set up, in concentrations enabling their physical observation. The linear electron accelerator of the Hebrew University of Jerusalem, which is used, forms up to... 

The rapid-freezing EPR data obtained in pulse radiolysis experiments had been interpreted by half-site reactivity In the meantime preparations have, however, been obtained with a definitely higher specific activity (second-order rate constant... 

X 10 against 2.4x 10 M s" for the preparations used in the pulse radiolysis experiments) so that the half-site reactivity has been seriously questioned by the presence of inactive enzyme in the earlier experiments Large differences in specific activity (up to a factor of two) and in the ability to protect mouse bone marrow stem cells against X-irradiation have been reported for five SOD preparations... 

An alternate reduction and oxidation of Cu by superoxide anions Scheme 3) followed from pulse radiolysis experiments value (pH 7.0) of Cu in BESOD... 

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