Pulse radiolysis, and

The one-electron reduction of thiazole in aqueous solution has been studied by the technique of pulse radiolysis and kinetic absorption spectrophotometry (514). The acetone ketyl radical (CH ljCOH and the solvated electron e were used as one-electron reducing agents. The reaction rate constant of with thiazole determined at pH 8.0 is fe = 2.1 X 10 mole sec in agreement with 2.5 x 10 mole sec" , the value given by the National Bureau of Standards (513). It is considerably higher than that for thiophene (6.5 x 10" mole" sec" ) (513) and pyrrole (6.0 X10 mole sec ) (513). The reaction rate constant of acetone ketyl radical with thiazolium ion determined at pH 0.8 is lc = 6.2=10 mole sec" . Relatively strong transient absorption spectra are observed from these one-electron reactions they show (nm) and e... 

The polarographic half-wave reduction potential of 4-nitroisothiazole is -0.45 V (pH 7, vs. saturated calomel electrode). This potential is related to the electron affinity of the molecule and it provides a measure of the energy of the LUMO. Pulse radiolysis and ESR studies have been carried out on the radical anions arising from one-electron reduction of 4-nitroisothiazole and other nitro-heterocycles (76MI41704). 

JOVANOVIC s V, HARA Y, STEENKEN s and SIMIC M G (1995) Autioxidant potential of gaUocatechins. A pulse radiolysis and laser photolysis study, J Am. Chem Soc, 117, 9881-88. 

In studies of this kind, methods developed in radiation chemistry and photochemistry are often applied The methods of pulse radiolysis and flash photolysis allow one to investigate the mechanism of reactions in which free radicals, electrons and positive holes are the intermediates. In order to understand the mechanisms of processes that occur on colloidal particles it is important to know how free radicals... 

Adams, G.E. and Redpath, J.L. (1974). Selective free-radical reactions with proteins and enzymes pulse radiolysis and inactivation studies on papain. Int. J. Badiat. Biol. 25, 129-136. 

Cabelli, D.E. and Bielski, B. (1983). Kinetics and mechanism for the oxidation of ascorbic acid (ascorbate by HO2/O2 radicals. A pulse radiolysis and stopped-flow photolysis study. J. Phys. Chem. 87, 1809. 

Oxidizing reagent TIOH+ was generated by pulse radiolysis and direct oxidation of ODN by TIOH+ was completed within 20 jus [46] (Scheme 7, path a). 

The radical cations of urazole-annelated azoalkanes 65 were generated by pulse radiolysis and the transients characterized spectrally and kinetically by time-resolved optical monitoring. The initial distonic 1,3 radical cations 66 were detected, and the methyl-substituted 66 further deprotonates to radical 67 (Scheme 1) <1997JA10673>. 

With the advent of picosecond-pulse radiolysis and laser technologies, it has been possible to study geminate-ion recombination (Jonah et al, 1979 Sauer and Jonah, 1980 Tagawa et al 1982a, b) and subsequently electron-ion recombination (Katsumura et al, 1982 Tagawa et al, 1983 Jonah, 1983) in hydrocarbon liquids. Using cyclohexane solutions of 9,10-diphenylanthracene (DPA) and p-terphenyl (PT), Jonah et al. (1979) observed light emission from the first excited state of the solutes, interpreted in terms of solute cation-anion recombination. In the early work of Sauer and Jonah (1980), the kinetics of solute excited state formation was studied in cyclohexane solutions of DPA and PT, and some inconsistency with respect to the solution of the diffusion equation was noted.1... 

In a study of long range ET between aromatic donor (biphenyl) and acceptor molecules separated by steroid spacers [39], pulse radiolysis and electron beam techniques have been used for the injection of electrons (Closs and Miller, 1988 Closs et al., 1989 Liang et al, 1990). Here, the reaction rates (observed by changes in the absorption spectra) pass through a... 

The capacity of cyclic ligands to stabilize less-common oxidation states of a coordinated metal ion has been well-documented. For example, both the high-spin and low-spin Ni(n) complexes of cyclam are oxidized more readily to Ni(m) species than are corresponding open-chain complexes. Chemical, electrochemical, pulse radiolysis and flash photolysis techniques have all been used to effect redox changes in particular complexes (Haines McAuley, 1982) however the major emphasis has been given to electrochemical studies. 

AK Pikaev, SA Kabakchi, IE Makarov, BG Ershov. Pulse Radiolysis and its Application. Moscow Atomizdat, 1980, pp 3-290 [in Russian]. 

The systems that we investigated in collaboration with others involved intermolecular and intramolecular electron-transfer reactions between ruthenium complexes and cytochrome c. We also studied a series of intermolecular reactions between chelated cobalt complexes and cytochrome c. A variety of high-pressure experimental techniques, including stopped-flow, flash-photolysis, pulse-radiolysis, and voltammetry, were employed in these investigations. As the following presentation shows, a remarkably good agreement was found between the volume data obtained with the aid of these different techniques, which clearly demonstrates the complementarity of these methods for the study of electron-transfer processes. 

In a first type of systems, redox centers are randomly distributed in a rigid matrix, glass or polymer [73, 74, 75], Donor or acceptor centers are initially created photochemically or by pulse radiolysis, and the study of the return to equilibrium of the system allows the determination of the law k(R) giving the rate variation as a function of the intercenter distance R. The experimental data are well described by an exponential law, which is considered as reflecting an exponential variation of the electronic factor ... 

Transients such as OJ or HO can be generated in solution by pulse radiolysis of O2. If such solutions are contained in one syringe of a stopped-flow apparatus they may be mixed with substrate and the final mixture examined spectrally. For flow experiments these transients must, of course, have lifetimes longer than a few millisecond. For the examination of more labile transients, production may be by laser photolyses or pulse radiolysis, and the substrate under examination must be then incorporated in the pulsed solution. Care has now to be taken that substantial amounts of the substrate are not lost (by reaction) as a result of the pulse. 

Ni(II) by strong oxidants, such as OH, Br and (SCN), produced by pulse radiolysis and flash photolysis. Rate constants are 10 M" s for oxidation by OH and Brf and = 10 M s for (SCN)f Ref. 259. The most popular means of production in both aqueous and nonaqueous solution is electrolytic, jjjg ligands which stabilize Ni(III) are cyanide, deprotonated peptides, amines and aminocarboxylates, a-diimines and tetraaza macrocycles, including porphyrins. Low spin d Ni(III) resembles low spin Co(II). The kinetics of the following types of reactions have been studied ... 

The kinetics of myoglobin oxidation and reduction have been studied by a variety of experimental techniques that include stopped-flow kinetics, pulse radiolysis, and flash photolysis. In considering this work, attention is directed first at studies of the wild-type protein and then at experiments involving variants of Mb. 

Tamba, M. and Torreggiani, A. (1999). Hydroxyl radical scavenging by carnosine and Cu (ll)-carnosine complexes A pulse-radiolysis and spectroscopic study. Int. ]. Radiat. Biol. 75,1177-1188. 

The UV absorption spectra of radical cations such as 87 have received attention, and the ESR spectra have been studied and in some cases interpreted. Rate constants for the one-electron reduction of diquat and the salts 82 (n = 3) and 82 (n = 4) have been determined by pulse radiolysis, and kinetic studies involving reactions of the diquat radical cation at hydrogen-evolving metal electrodes have been... 

The results in this discussion will include those from our laboratory and experiments on electron solvation from other laboratories. The experiments that were done at Argonne made use of the stroboscopic pulse radiolysis technique, which will be discussed below. Experiments from other laboratories have made use of pulse radiolysis and laser photolyis techniques for the measurement of electron solvation. 

With the development of the picosecond pulse radiolysis, the kinetics data of the geminate ion recombination have been directly obtained. The history of picosecond and subpicosecond pulse radiolysis is shown in Fig. 7. Very recently, the first construction of the femtosecond pulse radiolysis and the improvement of the subpicosecond pulse radiolysis started in Osaka University. 

Both Construction of the First Femtosecond Pulse Radiolysis and Improvement of the Subpicosecond Pulse Radiolysis started in Osaka University (2002) ... 

Figure 7 History of picosecond and subpicosecond pulse radiolysis and the start of construction of the first femtosecond pulse radiolysis.

Further detailed kinetics of the geminate recombination of electrons and positive ions and their application to the advanced technology will be studied by higher time resolution of the femtosecond pulse radiolysis and both by the higher S/N ratio and the wider wavelength monitoring light of the improved subpicosecond pulse radiolysis shown in Fig. 7. 

Pulse radiolysis and pulsed laser methods are powerful tools to study the reactions at the interface between clusters and solution, such as fast heterogeneous catalytic processes, or transfer of the charges generated inside the particle. 

Pulse Radiolysis and Pulse Radiolysis-Laser Flash Photolysis... 

Table 1 lists some of the binding constants and rate constants measured for the reaction of CO2 with redox-active molecules. Various techniques have been used to measure these constants including cyclic voltammetry, pulsed radiolysis, and bulk electrolysis followed by UV-visible spectral measurements. The binding constants span an enormous range from less than 1 to 10 M [13-17]. Co(I) and Ni(I) macrocyclic complexes have been studied in some detail [13-16]. For the cobalt complexes, the CO2 binding constants K) and second-order rate constants for CO2 binding (kf) are largely determined by the Co(II/I) reduction potentials... 

Pagsberg, P., O. J. Nielsen, and C. Anastasi, Gas Phase Studies in Atmospheric Chemistry Using Pulse Radiolysis and Transient Absorption Spectroscopy, in Spectroscopy in Environmental Science (R. J. H. Clark and R. E. Hester, Eds.), Chap. 6, Wiley, 1995. 

In principle, absorption spectroscopy techniques can be used to characterize radicals. The key issues are the sensitivity of the method, the concentrations of radicals that are produced, and the molar absorptivities of the radicals. High-energy electron beams in pulse radiolysis and ultraviolet-visible (UV-vis) light from lasers can produce relatively high radical concentrations in the 1-10 x 10 M range, and UV-vis spectroscopy is possible with sensitive photomultipliers. A compilation of absorption spectra for radicals contains many examples. Infrared (IR) spectroscopy can be used for select cases, such as carbonyl-containing radicals, but it is less useful than UV-vis spectroscopy. Time-resolved absorption spectroscopy is used for direct kinetic smdies. Dynamic ESR spectroscopy also can be employed for kinetic studies, and this was the most important kinetic method available for reactions... 

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