Pulse radiolysis studies

Second-order rate constants, 10 1 mol s, for the intermolecular reduction of [Co i(NH3)sX] complexes by pulse-radiolytically generated /J-OaNCeHiCOa (L ) can be compared with the value for the intramolecular electron transfer, ki = 2.6 X10 s , in carboxyl-bonded [Co i (NH3)5L]+ if a pre-equilibrium encounter complex is assumed and rate-determining electron transfer 

The reaction of OH with [(NH3)6Co py] produces a reactive transient with a second-order rate constant of 6.5 x 10 1 mol- s- (pH = 5.2). The absorption spectrum of this transient has a maximum at 320 nm (e = 18001 mol cm ) and is similar to the spectrum obtained in the radiolysis of free pyridine. It is proposed that the hydroxyl radical adds to the pyridine ligand to form a ligand radical co-ordinated to the Co centre. This species undergoes intramolecular redox to yield Co and pyOH with a rate constant of 6.0 s.  

Pulse radiolysis of solutions of anisole produces the anisole radical cation which is characterized by two intense absorption bands at. max = 280 nm (e = 7400 ImoHcm- ) and Amax = 430nm (e = 32001 moH cm. At pH 1.0, this species oxidizes iron(ii) to regenerate anisole with a rate constant of 6 x 10 1 mol  

A series of methoxylated benzene derivatives react with TF+ and Ag2+, generated by the action of OH on T1+ and Ag+ respectively, to form the radical cations (44). For anisole, the rate constants for M + = TP+ and Ag + are 5 x 10 and 3.8 x 10 1 mol s , and these values depend little on further substitution on the benzene ring. Subsequent dimerizations of the radicals proceed with rate constants between 4x 10 and 1 x 10 1 mol s depending on the relative positions of the methoxy-groups. 

Conductance and optical measurements on the reaction of OH with T1+ indicate that above pH 4 significant amounts of T10H +, absorbing at 360 nm, are formed  

Extensive compilations of rate constants for the reactions of metal ions in unusual valency states and of inorganic free radicals in aqueous solution have appeared, as well as short reviews on pulse radiolysis studies in general chemistry and on complexes of metal ions in unstable oxidation stages.  

Buxton and R. M. Sellers, Compilation of Rate Constants for the Reactions of Metal Ions in Unusual Valency States , NSRDS - NBS 62. 

Ross and P. Neta, Rate Constants for Reactions of Inorganic Radicals in Aqueous Solutions , NSRDS - NBS 65. 

—Combined conductivity and kinetic spectroscopy measurements lead to the conclusion that the bimolecular reaction between two CO3— radicals involves transfer of 0  

This is based on pH-dependent changes in conductivitivy which correlate with the rate of hydrolysis of CO 2 in alkaline solution. Other reactions in which CO 2 is formed by this mechanism are between COs and NO2, SOs, or CHg. In the last example a long-lived intermediate (/1/2 5 s), postulated to be CH30C02, is formed  

Adamcikova and L. Treindl, Coll. Czech. Chem. Comm., 1974, 39, 1264. 

Rearrangement within the dimer then takes place, with a photochemically accelerated reaction as the final step. Absorption spectra of the intermediates have been obtained. In contrast, the reduction of haemin by e q or MeCHO proceeds via a direct redox reaction involving a single-step transfer from Fe to Fe.  

The oxidized metal complexes are considered to be outer-sphere. In the pulse radiolysis of Fe sulphate solutions, oxidation to iron(iii) complexes is observed. In the 

spectrum of the Cu ion has been measured in formate and in methanol solutions. The reaction of -OH with Cl has been investigated and the series of equilibria deriving from the initial reaction has been characterized. The scheme may be represented as 

Absorption spectra of both CI2- and HOCl have been measured in the range A = 230—450 nm. Cl2 and Cl- oxidize Fe, the reactions being studied by the pulse radiolysis of solutions containing Fe(C104)2 and NaCl. It is not possible, 

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An interesting example of the N(9)-C(8) prototropic tautomerism has been reported for the caffeine radical by pulse radiolysis studies in aqueous solution the transformation of the heteroatom-protonated electron adduct 25 into the carbon-protonated tautomer 26 occurred spontaneously in neutral media [95JCS(F)615]. 

In pulse radiolysis studies, sulfonyl radicals have normally been generated by dissociative electron capture using sulfonyl chlorides as substrates, namely15. 

In pulse radiolysis studies it is feasible to eliminate undesired radical reactions by the use of "scavengers". For example, to produce a totally reducing system simple aliphatic alcohols are added and the ensuing reaction... 

In marked contrast there exists a volumnous literature on pulse radiolysis studies of nitric acid solutions (9). The NO3 radical has been identified as a major product although the mechanism of formation is still a matter of debate. While a number of reactions of this radical have been reported (10) there has evidently not been any pulse radiolysis studies of reactions with Pu ions. 

The skillful and dedicated collaborative efforts of members of the ANL Chemistry Division Radiation Chemistry Group, S. Gordon, W. Mulac and K. H. Schmidt have provided not only the technical expertise but also continuing intellectual stimulation which has made the pulse radiolysis studies possible. 

Baral S, Fojtik A, Weller H, Henglein A (1986) Photochemistry and radiation chemistry of coUoidal semiconductors. 12. Intermediates of the oxidation of extremely small particles of cadmium sulfide, zinc sulfide, and tricadmium diphosphide and size quantization effects (a pulse radiolysis study). J Am Chem Soc 108 375-378... 

JOVANOVIC s V, HARA Y, STEENKEN s and SIMIC M G (1997) Autioxidant potentials oftheaflavines. A pulse radiolysis study, J Am Chem Soc, 119, 5337—43. 

Kemp and coworkers employed the pulse radiolysis technique to study the radiolysis of liquid dimethyl sulfoxide (DMSO) with several amines as solutes [triphenylamine, and N, A, A, N -tetramethyl-p-phenylenediamine (TMPD)]. The radiolysis led to the formation of transient, intense absorptions closely resembling those of the corresponding amine radical cations. Pulse radiolysis studies determine only the product Ge, where G is the radiolytic yield and e is the molar absorption. Michaelis and coworkers measured e for TMPD as 1.19 X 10 m s and from this a G value of 1.7 is obtained for TMPD in DMSO. The insensitivity of the yield to the addition of electron scavenger (N2O) and excited triplet state scavenger (naphthalene) proved that this absorption spectrum belonged to the cation. 

Flash Photolysis and Pulse Radiolysis Studies Non-linear Optical Effects 142... 

It is known from pulse radiolysis studies that SOj and S O are formed by SO radicals in homogeneous solution in the ratio 2 1. The fact that practically the same... 

In a pulse radiolysis study of solutions of CdS of different particle size, the rate of reaction of the OH radical with the colloidal particles was studied as well as the absorption spectrum of the products The hydroxyl radical reacts on its first encounter... 

In the pulse radiolysis studies on the reaction of MV with TiOj, the sol contained propanol-2 or formate and methyl viologen, MV Ionizing radiation produces reducing organic radicals, i.e. (CH3)2COH or C02 , respectively, and these radicals react rapidly with MV to form MV. The reaction of MV with the colloidal particles was then followed by recording the 600 nm absorption of MV . The rate of reaction was found to be slower than predicted for a diffusion controlled reaction. 

Pulse radiolysis studies showed that the rate of the reaction of MV with a-Fc203, in which an electron is transferred to the colloidal particles, is slower than predicted for a diffusion controlled reaction. For pH > 8, the reaction is incomplete as the reverse reaction Fe203 - - - Fe203 - - MV takes place more efficiently... 

Forni, L.G., Packer, J.E., Slater, T.F. and Willson, KL. (1983). Reactions of the trichloromethyl and halothane derived peroxyl radicals with unsaturated fatty acids a pulse radiolysis study. Chem. Biol. Interact. 45, 171-177. 

In general, reduction potentials of nucleobases have been studied much less than their oxidation potentials, and in particular water-based data are rather lacking [2, 35]. We therefore listed the available polarographic potentials measured in dimethylformamide and data obtained from pulse radiolysis studies or fluorescence quenching measurements. From the data in Table 1, it is evident that the pyrimidine bases are most easily reduced. The reduction potential of the T=T CPD lesion is close to the estimated value of the undamaged thymine base [34, 36]. 

Monomeric platinum(III) complexes have been observed frequently as transient species in electrochemical or pulse radiolysis studies and they are proposed as an intermediates in reductive elimination and oxidative addition reactions of platinum(IV) and platinum(II) respectively.382-388... 

The bimolecular rate constants were determined (Burke 2001) for the repair of carotenoid radical cations by trolox, ascorbic, ferrulic, and uric acids from the pulse radiolysis studies of carotenoids in aqueous micellar solutions (see Table 14.10). 

G. Gzapski and L.M. Dorfman, Pulse radiolysis studies. V. Transient spectra and rate constants in oxygenated aqueous solutions. J. Phys. Chem. 68, 1169-1177 (1964). 

Most of the kinetic models predict that the sulfite ion radical is easily oxidized by 02 and/or the oxidized form of the catalyst, but this species was rarely considered as a potential oxidant. In a recent pulse radiolysis study, the oxidation of Ni(II and I) and Cu(II and I) macrocyclic complexes by SO was studied under anaerobic conditions (117). In the reactions with Ni(I) and Cu(I) complexes intermediates could not be detected, and the electron transfer was interpreted in terms of a simple outer-sphere mechanism. In contrast, time resolved spectra confirmed the formation of intermediates with a ligand-radical nature in the reactions of the M(II) ions. The formation of a product with a sulfonated macrocycle and another with an additional double bond in the macrocycle were isolated in the reaction with [NiCR]2+. These results may require the refinement of the kinetic model proposed by Lepentsiotis for the [NiCR]2+ SO/ 02 system (116). 

Tausch-Treml, R., Henglein, A., and Lilie, J., Reactivity of silver atoms in aqueous solution II a pulse radiolysis study, Her. Bunsen-Ges. Phys. Chem., 82,1335, 1978. 

D. Lawless, N. Serpone, D. Meisel, Role of OH. radicals and trapped holes in photocatalysis. A pulse radiolysis study,... 

Henglein A, Tausch-Treml R (1981) Optical absorption and catalytic activity of subcolloidal and colloidal silver in aqueous solution a pulse radiolysis study. J Colloid Interface Sci 80 84-93... 

Several studies have reported the influence of nitroimidazole derivatives on biological systems. Thus the influence of Misonidazole, l-(2-nitro-l-imidazoyl)-3-methoxy-propan-2-ol, on strand breaking in calf thymus DNA under ionizing radiation conditions has been assessed70. Pulse-radiolysis studies of nitroheterocyclic compounds have examined... 

Coulter ED, Emerson JP, Kurtz DM, Jr, Cabelli DE. 2000a. Snperoxide reactivity of rubredoxin oxidorednctase (desulfoferrodoxin) from Desulfovibrio vulgaris a pulse radiolysis study. J Am Chem Soc 122 11555-6. 

The characterization, redox properties, and pulse radiolysis study of manganese(III) complexes of type [MnLCy (where L = cyclam, meso-, and rac-5,7,7,12,14,14-hexamethylcyclam (tet a and tet b, respectively)) have been reported." An X-ray crystal structure of the meso-5,l,l, 2, A, A-hexamethyl-l,4,8,ll-tetraazacyclotetradecane complex shows that the coordination geometry of the tet a complex is close to octahedral with the macrocycle coordinated equatorially and the chlorides occupying irons axial sites. 

A pulse radiolysis study of the reaction between aqueous solvated electrons and benzyltrimethylammonium ions shows that dissociative electron transfer occurs to generate the benzyl radical, identified by uv-spectroscopy. No detectable intermediate is formed [40]. 

By a pulse radiolysis study, both the mechanism and corresponding rate constants of the formation of the transA,i dihydroxy-l,2-dithiane radical anion were quantitatively determined <1997JA5735, 1987ZNC134> the reaction was monitored by ultraviolet-visible (UV-Vis) spectroscopy. 

Pulse radiolysis is of great importanee in the understanding of gas-phase reactions [1-3]. The results obtained are also useful for understanding condensed phase reactions. The objectives of pulse radiolysis studies in the gas phase are divided into two parts. One is to understand the fundamental processes, in particular, early processes in radiolysis. The other is to make an important contribution, as one of the powerful experimental methods, to gas-phase collision dynamics studies. Recent advances in the latter studies are surveyed in this paper those in the former studies are not included here. The above-mentioned objectives are, however, closely related with one another in terms of the following interface relationships. New information obtained from the latter studies is useful for understanding the fundamental processes in radiolysis, whereas that from the former studies is an important source of new ideas and information in collision dynamics studies. 

Advances in pulse radiolysis studies in the gas phase have been summarized in several review papers. In a comprehensive review by Sauer [4], a review presented by Firestone and Dorfman [5] in 1971 was referred to as the first review on gas-phase pulse radiolysis. Experimental techniques and results obtained were summarized by one of the present authors [6], with emphasis on an important contribution of pulse radiolysis to gas-phase reaction dynamics studies. Examples were chosen by Sauer [7] from the literature prior to 1981 to show the types of species that were investigated in the gas phase using pulse radiolysis technique. Armstrong [8] reviewed experimental data obtained from gas-phase pulse radiolysis together with those from ordinary steady-state radiolysis. Advances in gas-phase pulse radiolysis studies since 1981 were also briefly reviewed by Jonah et al. [9], with emphasis on an important contribution of this technique to free radical reaction studies. One of the present authors reviewed comprehensively the gas-phase collision dynamics studies of low-energy electrons, ions, excited atoms and molecules, and free radicals by means of pulse radiolysis method [1-3]. An important contribution of pulse radiolysis to electron attachment, recombination, and Penning collision studies was also reviewed in Refs. 10-15. 

Fast pulse radiolysis studies have shown that geminate recombination occurs on the picosecond time scale [12,13]. Bartczak and Hummel [14] predicted that for -dodecane, 82% of the geminate ions still remain at 5 psec for 1 MeV irradiation. Future accelerators, with pulses of a few picoseconds length, may soon provide experimental measurements of Gtot directly. 

Early pulse radiolysis studies of alkanes at room temperature showed that the solvated electron absorption begins around 1 pm and increases with increasing wavelength to 1.6 pm for -hexane, cyclohexane, and 2-methylbutane [77]. More complete spectra for three liquid alkanes are shown in Fig. 4. The spectrum for methylcyclohexane at 295 K extends to 4 pm and shows a peak at 3.25 pm [78]. At the maximum, the extinction coefScient is 2.8 x 10 cm The spectrum for 3-methyloctane at 127 K, shown in Fig. 4, peaks around 2 pm. The peak for methylcyclohexane is also at 2 pm at lower temperature. Recently, the absorption spectra of solvated electrons in 2-methylpentane, 3-methylpentane, cA-decalin, and methylcyclohexane glasses have been measured accurately at 77 K [80]. For these alkanes, the maxima occur at 1.8 pm, where the extinction coefScient is 2.7 x 10 cm. ... 

The stronger absorption at lower temperatures can be attributed to several factors. One is that the equilibrium between quasi-free and trapped electrons shifts to favor trapped electrons as the temperature is lowered for these liquids. Another is that homogeneous recombination of electrons with positive ions is slower at the lower temperatures and therefore occurs to a lesser extent during the pulse, which, for the pulse radiolysis studies, was typically 10 to 20 nsec. The rate constant, k, for electron recombination with positive ions, in most nonpolar liquids, is given by ... 

PICOSECOND AND SUBPICOSECOND PULSE-RADIOLYSIS STUDIES OF GEMINATE ION RECOMBINATION IN LIQUID HYDROCARBONS... 

Subpicosecond Pulse-Radiolysis Studies of Geminate Ion Recombination... 

There are many excellent books and reviews on the structure and reactions of secondary radical ions generated in radiolytic and photolytic reactions. Common topics include the means and kinetics of radical ion production, techniques for matrix stabilization, electronic and atomic structure, ion-molecule reactions, structural rearrangements, etc. On the other hand, the studies of primary radical ions, viz. solvent radical ions, have not been reviewed in a systematic fashion. In this chapter, we attempt to close this gap. To this end, we will concentrate on a few better-characterized systems. (There have been many scattered pulse radiolysis studies of organic solvents most of these studies are inconclusive as to the nature of the primary species.)... 

Hermann, R. Brede, O. Mehnert, R. Energy Transfer from Alkane Singlets and Quenching of AlkaneFluorescences by Alkyl Chlorides. A. Pulse Radiolysis Study. Proceedings 5th Tihany Symposium on Radiation Chemistry Dobo, J. Hedvig, P. Schiller, R., Eds. Akademiai Kiado Budapest, 1983 503 pp. 

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