Pulse radiolysis aqueous solution

Studies of proton transfers from carbon with f1/2 less than one microsecond are quite rare. The ionization of hydrogen cyanide in aqueous alkaline solution has been studied [20] using the ultrasonic stationary method which is applicable to reactions with tl/2 in the range 10 5 to 10 9 sec. Several reactions of benzyl carbanion having f 1/2 in the range 10-6—5 x 10-8 sec have been studied in tetrahydrofuran. The carbanion was generated by pulse radiolysis of solutions of dibenzyl mercury and its subsequent reaction with water and alcohols was followed spectrophotometrically [21]. 

Radiation Chemistry of Solvents Water. The successful design of a radiation chemistry experiment depends upon complete knowledge of the radiation chemistry of the solvent. It is the solvent that will determine the radicals initially present in an irradiated sample, and the fate of all these species needs to assessed. Among the first systems whose radiation chemistry was studied was water, both as liquid and vapor phase, as discussed by Gus Allen in The Story of the Radiation Chemistry of Water , contained in Early Developments in Radiation Chemistry (8), Water is the most thoroughly characterized solvent vis-a-vis radiation chemistry. So to illustrate the power of radiation chemical methods in the study of free radical reactions and electron-transfer reactions, I will focus on aqueous systems and hence the radiation chemistry of liquid water. Other solvents can be used when the radiation chemistry of the solvent is carefully considered as noted previously, Miller et al. (I) used pulse radiolysis of solutions in organic solvents for their landmark study showing the Marcus inversion in rate constants. 

The formation of chromium-carbon a-bonds in aqueous media has been investigated, the specific rates of reaction of chromium(ii) with aliphatic radicals being measured. Pulse radiolysis of solutions of Cr and organic molecules generates OH and H radicals which react with the organic species... 

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... 

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]. 

Complexes of cations in unstable oxidation states in aqueous solutions as studied by pulse radiolysis. D. Meyerstein, Acc. Chem, Res., 1978,11,43-48 (95). 

Meissner and coworkers36 studied the pulse radiolysis of aqueous solutions of dimethyl sulfoxide. It was found that hydrated electrons react with DMSO with a rate constant of... 

Veltwisch and colleagues45 studied the reaction of OH with several sulfoxides by pulse radiolysis using electrical conductivity for the detection of formation or disappearance of ions. Pulse radio lysis of N20-saturated aqueous solution of DMSO (10-3m) leads to a decrease in conductivity at basic pH (pH = 9.0) and an increase in conductivity at acidic pH (pH = 4.4). This is explained by the reactions... 

They measured the formation of ionic species in the pulse radiolysis of a 10"3 m MTMSO aqueous solution saturated by N20 gas at pH 5.6 by conductivity detection and found an increase in conductivity. Assuming the molar conductivity of CH3SCH2S02 to be the same as that measured for CH3S02- 45, it is found that G(CH3SCH2S02") = 2.7. 

Nelson54 studied the products of radiolysis of aqueous solution by variable-field CIDNP pulse radiolysis. On the basis of the chemical shifts the following products were identified methyl methanesulfinate, methanol, l,2-bis(methylsulfinylethane) [CH3S(0)CH2CH2S(0)CH3], dimethyl sulfone, dimethyl sulfide, methane and ethane. The high field polarization was used to study the mechanism of formation of polarized products. 

The application of techniques of pulse radiolysis offers the potential to determine rates of primary radiolysis induced reaction processes. This knowledge can be of great value in the determination of redox processes of Pu ions occurring in a wide variety of aqueous solutions. As a matter of fact, such information is essential to a prediction of the Pu oxidation states to be expected in breached repository scenarios. For an... 

By pulse radiolysis of nitrous oxide-saturated aqueous solutions of ferricyanide (2 X 10 " M) and various alcohols (0.1 M), Adams and Willson " were able to obtain absolute rate coefficients for the ferricyanide oxidation of the radicals derived from the alcohols by attack of the solvent irradiation product, OH-. 

The standard reduction potentials determined in aqueous solution give hierarchies slightly different from the antioxidant hierarchy established in DMF. For the potential determined by pulse radiolysis the ordering according to tendency of regeneration is (Jovanovic et al, 1994) ... 

Sumiyoshi and coworkers studied the radiolysis of aqueous solution of methyl methylthiomethyl sulfoxide [ H3S(0) H2S H3 MTMSO] at various pH by pulse radiolysis. They found that the reaction of e with MTMSO (in the presence of 1M t-butyl alcohol to scavenge OH" radicals) leads to formation of a transient with a broad absorption band of = 375 nm. The absorbance at 375 nm as a function of pH are of S shape, indicating an equilibrium due to reaction with H. Similar to the finding in dimethyl sulfoxide they suggested the scheme. 

While aqueous solutions mean only dilute solutions, mixtures can be any proportion of HjO and DMSO. Cooper and coworkers found in the pulse radiolysis of H2O/DMSO mixtures two easily resolvable absorption bands at wavelengths >400nm. One band corresponds to the oxidizing species with a maximum at 600 nm and a relatively long half-life (1 to 4/is). The second band with higher wavelength (720-1500 nm) and shorter half-life is attributed to the solvated electrons. 

In a related manner, gamma radiolysis of tetrazolium salts also yields formazans.256,257 Pulse radiolysis in aqueous solutions leads to tetrazole... 

Fig. 5 Transient absorption spectra of PtzODNl obtained at 1 f.is, 5 f.is, and 50 f.is during pulse radiolysis of N20-saturated aqueous solution containing 0.2 mM PtzODNl (strand cone.), 20 mM pH 7.0 Na phosphate buffer, and 1 mM T12S04... 

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). 

The pulse radiolysis technique gives a direct way for measuring the hydrated electron yield. To get the stationary yield, one can simply follow the electron absorption signal as a function of time and, from the known value of the extinction coefficient (Table 6.2), evaluate g(eh). Alternatively, the electron can be converted into a stable anion with a known extinction coefficient. An example of such an ion is the nitroform anion produced by reaction of eh with tetrani-tromethane (TNM) in aqueous solution ... 

J. Rabani, W.A. Mulac, and M.S. Matheson, The pulse radiolysis of aqueous tetranitromethane. I. Rate constants and the extinction coefficient [absorptivity] of aq-. II. Oxygenated solutions. J. Phys. Chem. 69, 53-70 (1965). 

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). 

Aqueous alkaline luminol solutions can be excited to chemiluminescence by pulse radiolysis, the only additional requirement being oxygen 119h The suggested mechanism is that hydroxyl radicals attacking luminol monoanions, followed by reaction of the luminol radical anion thus formed with oxygen ... 

Michael and Hart10 found that the reaction of OH radicals (formed by pulse radiolysis of aqueous solutions saturated with N20) with 1,3- and 1,4-cyclohexadienes leads to formation of an intermediate absorbing at 310 nm. In the case of 1,4-cyclohexadiene, another band at A, < 240 nm was also found. In this system there are both H atoms and OH radicals, however the yield of the OH radicals is 10 times higher than that of the H- atoms. Michael and Hart10 assumed that the band at 310 nm is due to CeWi ... 

Pulse radiolysis of N20-saturated aqueous solution of 1,4-cyclohexadiene leads to formation of three radicals, two by addition of either OH or H atoms to give the cyclohexenyl radicals 3 and 4 (equation 12 and 13) and one by abstraction of H atoms (equation 14). The last one, the cyclohexadienyl radical, can exist in two mesomeric forms (5a and 5b). Fessenden and Schuler16 found that the spin density of the cyclohexadienyl radical was highest at the central atom, i.e. form 5a is the predominant one. 

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. 

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... 

Properties of Transition Metal Complexes with Metal-Carbon Bonds in Aqueous Solutions as Studied by Pulse Radiolysis... 

The second-order rate constant for oxidation of Fe(CN)g by OH" radicals, produced by low-intensity-pulse radiolysis of water, varies with pH as in the accompanying table. Determine the pA for acid dissociation of the OH" radical in aqueous solution. (This is difficult to obtain by any other method.)... 

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 ... 

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