Browsing by Author "Swallow, A. John"

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Oxidation of Ferrous Ions by an Aliphatic Dioxyl Radical
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (07), 1974) Butler, John; Jayson, Gerald G.; Swallow, A. John
1-Hydroxy-1-methylethyl radicals react with oxygen with a rate constant of 4.5 ± 0.5 × 109 dm3 mol–1 s–1. The resulting dioxyl radicals react with ferrous ions with a rate constant at 25°C of 1.7 ± 0.2 × 106 dm3 mol–1 s–1, entropy of activation + 99 J °C–1 mol–1. Pulse radiolysis data are consistent with the product of the reaction being a complex, Fe3+RO–2, which is in equilibrium with a bridge compound, Fe3+RO–2Fe2+. The complex disappears in a first order manner with a rate constant at 25°C of 3.85 ± 0.15 × 103 s–1, entropy of activation –82 J °C–1 mol–1. The bridge compound disappears in a first order manner with a rate constant at 25°C of 2.1 ± 0.1 × 104 s–1, entropy of activation –0.9 J °C–1 mol–1. The 1-hydroxy-1-methylethyldioxyl radical has a weak absorption with a peak at 250 nm. Fe3+RO–2 has a weak absorption extending through the visible region of the spectrum. Fe3+RO–2Fe2+ has a stronger absorption with a broad peak at 320 nm. 1-Hydroxy-1-methylethyl radicals react with ferric ions with a rate constant of 4.5 ± 0.5 × 108 dm3 mol–1 s–1.
Pulse Radiolysis Study of Protoferrihaem IX Intercalated in Sodium Dodecyl Sulphate Micelles
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (02), 1978) Evers, Edward L.; Jayson, Gerald G.; Swallow, A. John
Haemin intercalated in sodium dodecyl sulphate (SDS) micelles exists as monomer in an organic sphere of dimensions similar to that of cytochrome-c and thus provides a model which is closer to the biological molecule than any which has been studied hitherto. Hydrated electrons reduce intercalated haemin at pH 9.2 with k = 5.2x 10° dm3 mol-1 s-1. CH3CHOH radicals reduce it at pH 9.2 with k = 5.6x 108 dm3 mol-1 s~* and at pH 4 with k = 1.6x 10’ dm3 mol-1 s-1. Reduction is accompanied by spectroscopic changes in the haemin molecule at both pH 9.2 and 4, but at pH 9.2 additional changes take place afterwards over periods of several milliseconds. At pH 4.0 there are no additional changes. The final spectrum attained in both cases corresponds to the formation of reduced haemin in 100 % yield. The additional changes taking place after reduction in mildly alkaline solution are found to have an activation energy of 66.6 kJ mol-1. They are independent of pH in the range 9.2-10.7, and of added electrolyte in the range 0.05-0.2 mol dm-3. They arc attributed to conversion of OH- in reduced haemin into H2O, perhaps by protonation by water: [OH-Fei”(por)-H20]= + ca-q -> [OH-Fe"(por)-H2O]- I h2o [H2O-Fel'(por)-H2O]' + OH-. Corresponding changes are not seen at pH 4 because the hacmin exists as [H2O-Feni(por)-H2O]1' at that pH.
Reaction of Cob(i)alamin with Nitrous Oxide and Cob(in)alamin
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (2), 1977) Blackburn, Robert; Kyaw, Maung; Swallow, A. John
Cob(I)alamin (vitamin B12s) has been generated by pulse radiolysis of N2O-saturated solutions of cob(II)alamin (vitamin B12r) containing sodium formate. It reacts with N2O with rate constants in the range 200–1200 dm3 mol–1 s–1, depending on pH and buffer concentration. The final product is cob(II)alamin, formed in 100 % yield. The initial product is thought to be cob(III)alamin (vitamin B12a or B12h) but this does not build up to significant concentrations. Cob(III)alamin (vitamin B12a or B12h) reacts with cob(I)alamin with a rate constant of 3.2 × 107 dm3 mol–1 s–1 independent of pH in the range 5.8–11.0. Cyanocobalamin (vitamin B12) does not react with cob(I)alamin.