An inhibitor method for measuring the initiation rate is proposed for the system Fe3+ +
H202.The number of chains terminated by one C(NO& molecule was estimated in specific photochemical experiments and found to be unity. The initiation appeared to involve two processes. The first is proportional to the first power of ferric ion concentration, and the second to the second power. The rate constants and activation energies of these processes are determined. Allowance for the second initiation process permitted qualitative and quantitative description of various reported data on H202 decomposition rates over a wide range of Fe3+, H202, and H+ concentrations. C(N02)4 was used as inhibitor.
14) For reviews of the radlolytic method to generate unsolvated species at high pressures see the following: (a) P. Ausloos, Prog. React. Klnet., 5, 113 (1959); (b) "Ion-Molecule Reactions", J. L. Franklin, Ed., Plenum Press, New York, 1970; (c) P. Ausloos, S. G. Lias, and A. A. Scala, "Ion-Molecule Reactions In the Gas-Phase", American Chemical Society, New York, N.Y., 1970, p 264; (d) S. G. Lias, "Ion-Molecule Reactions In Radiation Chemistry" in "Interactions between Ions and Molecules", P.
The oxidation of ascorbic acid (AH2) and hydroquinone (QH2) by photolytically generated HO2•radicals was studied over a broad range of pH. The rate constants of the following processes were obtained[Formula: see text]and[Formula: see text]depending upon two different possible mechanistic interpretations.
When Compounds I and I1 of horseradish peroxidase in glycerol/water glasses at 77 K were irradiated with the light of a mercury lamp, some changes in optical spectra as well as the development of strong EPR signals of a free-radical type were detected. In case of photolysis of Compound I the light of wavelengths around 400nm was the most effective, while only short wavelength (1280nm) light affected Compound 11. The results of experiments with thawing and freezing the product of photolysis of Compound I (called Intermediate Y) provide further evidence for the suggestion that the ferric state of the heme iron is generated in the course of the photolysis. The quantum yields of the photolysis of Compound I at different wavelengths of irradiating light were obtained and mechanisms of the photolysis of Compounds I and I1 are proposed.
The one-electron oxidation of horseradish peroxidase compound II to compound I by sodium periodate was observed. The bimolecular rate constant for the NaIO4--compound II interaction is equal to 9.5 +/- 1 x 10(-3) M-1s-1 at room temperature. Irradiation, using ultraviolet light, of the solution containing compound II and persulfate in the presence of bicarbonate, chloride, or bromide, leads ot the fast accumulation of compound I due to the oxidative action of SO4, CO3, Cl2, and Br2 anion radicals, which are products of the photolysis.
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