The Pulse Radiolysis of Aqueous Tetranitromethane.¹ I. Rate Constants and the Extinction Coefficient of e_aq^-. II. Oxygenated Solutions

Abstract

Aqueous solutions of tetranitromethane (TNM), both deaerated and oxygenated, have been investigated by the technique of pulsed radiolysis. This system enabled the direct determination of ee6780, the extinction coefficient of the hydrated electron, at 5780 A. as 10,600 (±10%) Af-1 cm.-1. ee6780 is essential for evaluating rate constants previously determined as k/tam. Also from ee6780 we calculate Ge = 2.6 from values of Ge X ee67S0 in the literature. A number of rate constants were determined, including k(eaq~+ TNM) = 4.6 X 1010 Af-1 sec.-1, fc(H + TNM) = 5.5 X 108 Af-1 sec.-1, and k(eaq~+ NF-) = 3.0 X 1010 Af-1 sec.-1, where NFis the nitroform ion. Rate constants have also been measured for reaction of several organic radicals with TNM. In the presence of 02, k(02-+ TNM) was measured as 1.9 X 10® Af-1 sec.-1. fc(H02 + TNM) is less than 10-5 as large. Measurement of the effective k as a function of pH gave pK = 4.45 ± 0.25 for the dissociation, H02 H+ + 02-.(1) Based on work performed under the auspices of the U. S. Atomic Energy Commission.

Pulse radiolysis: evidence for the reaction of HO2 with NO2 in aqueous solution

“…The mechanism we propose requires that reactions [3] and [4] should compete with [2] for HO, and NO, in the rapid stage and influence the ob- 4), a s these authors also noted a slow build-up of nitroform over some minutes in the pulse radiolysis of oxygen saturated T N M solutions, probably attributable t o H 0 2 N 0 2 . If so, this would introduce a small error in the estimate of the pK of the HO, radical (4.45 f 0.25) which they deduced from their observations.…”

“…A possible explanation is that the species HOzNO, slowly deco~nposes as follows: so that the NO, and HO, so evolved at low concentration react nearly quantitatively in [I], [2], [4], and [S]. On this view HO,NO, might be regarded as somewhat analogous to the species H,03 which is formed by reaction of HO, with O H (I 3), but differs from H 0 , N 0 2 in that it slowly decomposes to unreactive products at a rate which varies with pH.…”

“…The rapid and delayed yields of nitroform in experiment 9 were G, = 2.45 and G, = 2.89, respectively. These may be compared with those calculated for reactions [2] and [3] (since we assume all the HO,NO, formed in the rapid stage ultimately yields nitroform in a delayed reaction) in competition with reaction [4] as G [2]c,llc, = 2.69 and G [3],,,,,, = 2.67, respectively, adopting the rate constants previously quoted (1) for /r3 (4 x 10' dm3 mol-' s-I) and /r, (101° dm3 mol-' s-I). In this case the apparent mass balance is reasonable, i.e., GI = 5.89, which is close to 6.…”

Superoxide Radical and Superoxide Dismutases

“…Thus, O 2 reduces tetranitromethane to the nitroformate anion (171) and oxidizes epinephrine to adrenochrome (163) and both of these indicating scavengers have been used (163). Tetranitromethane reacts with O 2 at neutral pH four orders of magnitude faster than does cytochrome c (171,172) and so gives an assay which is proportionately less responsive to inhibition by superoxide dismutase.…”

Oxidation of reduced Cu,Zn superoxide dismutase by molecular oxygen. A kinetic study

“…Measurements carried out at [TMNJ/[ECu(I)] > 10 showed that the nitroform ion, the one-electron-reduction product of tetranitromethane characterized by 6366 = 1.02x 104 M-l cm-1 (Rabani et al, 1965), was formed when ECu(I) was added to tetranitromethane solutions containing molecular 02. Taking into account the results of blank experiments, which showed a small Since in our experiments the concentration of superoxide dismutase was always higher than S ,Czm, and the O2,-generated in reaction (5) will react with the superoxide dismutase even at pH 4.8, where the spontaneous dismutation of 02--occurs at the highest rate (Czapski & Dorfman, 1964).…”